I do appreciate that, chowhound... Not always fun being the slow kid in the back of the class!! 
As for the "parallel" depiction, I'd say it's roughly specifics (some which we both already mentioned), leading into general observation - Lol! If that makes any sense at all??? 
... But here is something that made my brain really ache 
(and considering I'm still speaking "dates/timing" here, I hope I'm not too OT?!!): Various dates between original book/screenplay/movie are seriously screwy (IMHO). In the screenplay, Ennis and Jack's last go-around is sometime in 1981; afterwards, Ennis visits Jack's parents sometime in 1982 -- but in the original book, Jack and Ennis had their last meeting in May 1983! In my mind, the book timing makes much more sense, placing their last meet, and Jack's last visit home, in Spring, with the August/November fiasco coming up that same year; if the screenplay version is in Spring 1981 (later wouldn't make any sense considering all that's supposed to have happened between their last meeting and the death), leading to the next year, that leaves the "Deceased" postcard coming way later, meaning November already passed with Ennis showing no concern that Jack hadn't at least written him back??? (I don't believe that one bit.) So, trying to correlate the timing between book/screenplay/movie is sometimes quite a chore. 
And then in the screenplay, there is a point where either I'm not working with a full enough deck to get it or they simply weren't seeing straight at some point, with the dates going back and forth between 1971 (Ext: Riverton, WY / Ext: Childress, TX), 1969 (Int: TX / Int: Riverton, WY / Int: Childress, TX), 1973 (On the wall calendar behind Lureen), then back to 1969, at which juncture it seems to stop jumping around (or perhaps I've simply hit the wall of distinguishing ability!). Normally I would think they must be doing some kind of weird flashback sequence, but it doesn't seem to connect; and instead I feel like I must have somehow mistakenly slipped into an episode of "Sliders"! Was there an obvious point here that escapes me or were they merely missin' the meeting of minds that night?? Also, they seem to make it clear that it's one or two times a year that J & E get together, but then, likewise, I recall something, somewhere, about it being 3 or 4 times! I think the variance is important, but try askin' me where to find it, at this instance, and good luck with that... Just beyond this waking slumber's brainpower quota to give proper examples; but I know I heard, saw somethin' somewhere somehow! Lol!! 
I completely agree, JnE, that there are real problems with some of the dates in the published screen play. The major ones I deal with as footnotes to a timeline for Brokeback Mountain which I created some while ago. What I'm sending you as an addendum to this post is a somewhat slightly updated version of the one I posted on this board some time back.
Although, apart form one or two esential dates, the short story seems to float above time, the screen play and hence the movie is far more rooted in the passage of time. Not only do Jack and Ennis age as the movie progresses but there are all sorts of other time markers: dates on postcards and wall calendars, dates on banners, TV programmes and announcements, dates of the cars, trucks and their license plates, etc., etc.
Therefore, I think it's worthwhile to acknowledge all this sort of work that was put into the movie by creating a timeline for it but, given some of the screen play's dates, at times such efforts can be frustratingly confusing.
______________________________________________________________
ADDENDUM
A Timeline for Brokeback Mountain.
In the following timeline, ss=short story and sp=screen play. All
quotations are from "Brokeback Mountain:Story to Screenplay".
1941 K.E. del Mar born
1943 Jack and Ennis born (Sept.-Dec.)
1952. Ennis and K.E. forced to look at Earl's mutilated body by their
father
1957 ? Ennis's parents killed
1963:
May 7 Jack and Ennis meet
May 8 Full moon
May 24 Elk and potato dinner
June 7 TSN1. Full moon
June 8 TSN2
June. Ennis and Jack switch routines
June. Ennis and Jack move the sheep further up the mountains
July. Aguirre spying
July. Hailstorm and sheep tangle
August. Snow on August 13. Forced to leave Brokeback about a week or so
later. *1.
Nov. Ennis marries Alma Beers
1964:
Jan. Alma pregnant
spring: Ennis employed shovelling asphalt
spring: Ennis and Alma see "Surf Party" (1964)
spring: Jack returns to Brokeback
autumn: Alma jr. born
1965:
winter: Jenny born
1966:
Jan. Ennis, Alma and the two children living in the "little line cabin".
July 4. Alma, Ennis and the two children attend Independence Day
celebrations. By now, the family has presumably moved to the new apartment
over the laundromat in Riverton.
August. Jack meets Lureen at rodeo
1967:
Jan. ?Bobby born.
Sept 24 Jack and Ennis re-unite in Riverton
Sept 25-? Wyoming campsite
[1967-83:
"Years on years they worked their way through the high meadows and
mountain drainages, horse-packing into the Big Horns, Medicine Bows, south
end of the Gallatins, Absarokas, Granites, Owl Creeks, the Bridger-Teton
Range, the Freezeouts and the Shirleys, Ferisses and the Rattlesnakes,
Salt River Range, into the Wind Rivers over and again, the Sierra Madres,
Gros Ventres, the Washakies, Laramies, but never returning to Brokeback."
ss. p.17]
1971: *2
Girls on swing scene
Jack driving tractor scene.
1972:
July Ennis receives postcard from Jack ("See you in a couple of weeks")
[postmark: July, 1972.]
July/August Blue parka scene. 14 hour drive for Jack.
July/August Ennis leaves for Big Horn mountains. Almost forgets his tackle
box.
July/August Jack and Ennis meet up in the Big Horn Mountains. ["Jack comes
out of the tent, the intense pleasure of being with Ennis all over his
face." sp. p.58]
August/September Jack with Bobby probably driving one of the "new models"
Lureen mentions to Jack before he leaves for the Big Horns.
1973:
Alma: "We could still smarten up, head over to the church social" (sp.
p.60).An episode from "Kojack" is playing on the TV.
-
Ennis: "If you don't want no more of my kids, I'll be happy to leave you
alone." (sp. p.60)
1975:
Nov. 6 Alma and Ennis divorce. *3.
Nov. Jack drives up to be with Ennis. Rejected.
Nov. Jack goes to Mexico.
Dec. Jack meets up with Ennis? Jack says "see you next month, then..."
(sp. p.63) in the "rejection" scene. *3.
1976
April. Jack receives the "divorce" postcard. Drives up to be with Ennis.
Rejected.
April. Jack goes to Mexico.
May. Jack meets up with Ennis? Jack says "see you next month,
then" (sp.p.63) in the "rejection" scene. *3..
1977:
Nov. Thanksgiving weekend. The two Thanksgiving dinners.
1978:
Mountain scene. Jack suggests that Ennis might move to Texas.
-
Ennis meets Cassie.
-
Jack and Lureen have dinner with the Malones. [Banner behind bar reads
"Welcome to the 1978 Benefit Dinner, The Childress County Children's
Home"]
1979:
Bar scene where Cassie asks Alma Jr. "...your daddy ever gonna see fit to
settle down again?" (sp. p.77) [sp. notes that Alma is 15]
1983: *4.
May. Hail Strew River Drainage. Final time together:
(a) Jack: "tell you what...truth is, sometimes I miss you so bad I can
hardly stand it." (sp. p.80)
(b) Asleep in tent, Ennis curled around Jack.
(c) The quarrel. Jack: "come here...it's alright, it's all right...damn
you Ennis". (sp. p.83)
(d) Flashback to Brokeback, 1963. The Dozy Embrace.
(e) Jack watches Ennis's truck as it drives away.
July. ? Final scene with Cassie
August/Sept. ? Jack dies. *5.
October/early Nov. Ennis phone call to Lureen [Ennis's postcard to Jack
had proposed they meet at Pine Creek on Nov 7] *6.
Nov. ?Ennis visits the Twists
1984
spring: Alma Jr. visits Ennis. [Alma is 19]
June 5 Alma presumably marries Kurt.
NOTES:
*1 I prefer these dates with the first full moon we see occurring in May
and TSN1 taking place at the next full moon in June. I chose the May date
in part because, when Jack and Ennis are first going up the mountain, the
foliage has the very light green look of spring (May) rather than the
somewhat darker green of full summer (June). It also gives Jack and Ennis
a longer time together after TSN2 before they are forced to leave
Brokeback. But making everything a month - or full moon - later also
works.
*2. Editorial intervention is required here as the dates in sp. are very
mixed up. It has one scene - the girls on swing scene - which is dated
1971 - and then that is followed by 5 scenes dated 1969: (i) the
"piss-ant" scene; (ii) the arrival of Jack's postcard which is clearly
date stamped "July, 1972"; (iii) blue parka scene but wall calendar says
1973; (iv) Ennis forgets tackle; (v) Jack and Ennis in camp. Then comes
the scene where Jack shows Bobby how to drive which the sp. dates as 1972.
What I've done is to keep the swing scene in 1971 but, with the postcard
date as my guide, moved the remaining '69 scenes into 1972. This seems
to me to make a sensible chronological sequence but others may favour a
different solution.
*3 One possibility is that what the judge says here is an "interlocutory"
decree and not a final decree. The final decree would then have been
granted some months later - say, in March or April of the following year.
If Ennis sent Jack that postcard shortly after receiving the final decree,
then Jack would have probably driven up in April and his reference to
their meeting next month would point to May.
Another possibility is that the judge’s pronouncement is final but that
Ennis spends some time getting things sorted out before sending Jack that
postcard. This again could result in Jack’s driving up in April.
In general, a number of Brokies feel that it is much more likely that the
meeting referred to would take place in the spring and not in wintery
December. There is some textual support for this. In one of the earlier
scripts for Brokeback Mountain, Jack’s line reads: "I’ll see you first
week in June, then."
*4. With some reluctance, here I've used the dates found in the ss.
and not the dates found in the sp. The sp. dates I find confusing.
Here are some reasons:
(i). The sp. places the final confrontation in 1981. However, in both ss.
and sp. Lureen informs us that Jack was thirty nine when he died. So, even
if Jack is 20 when he first meets Ennis, as the sp. claims, not 19, as the
ss. suggests, the date surely should be 1982, not 1981.
(ii) Although the final confrontation is dated 1981 in the sp., Ennis's
phone call to Lureen in the sp.'s dating doesn't take place until 1982.
I've always assumed that the "deceased" postcard was returned to Ennis
before the November 7 date proposed by Ennis and that this is what led to
the phone call. I find it very difficult to believe that Ennis went to the
Pine Creek reunion, found out that Jack wasn't coming and only in
1982 got the "deceased" postcard and decided to phone Lureen.
(iii). The final two scenes - Ennis's visit to the Twists and Alma's visit
to him - are also both placed in 1982. However, with her marriage set for
June, it seems to me much more likely that she would visit her father in
the spring a month or two ahead of the date rather than in the depths of
winter to invite him to a marriage still at least six or seven months
away.
(iv). However, if other people have other solutions, or suggestions,
please pass them on. I for one, would be delighted to hear them. None of
this is set in stone.
*5. The exact time of Jack's death is unknown. Jack has presumably gone to
Lighning Flat for a few days before heading back to Texas after his May
meeting with Ennis which is when he must have said to his father that he
would be returning with "another fella" (sp. p.90). OMT then goes on to
say "...but like most of Jack's ideas it never come to pass". (sp. p.90).
Therefore, I think a fair amount of time must have passed between Jack's
offer and his death. If Jack had died shortly after his return to Texas,
surely OMT would have put it differently.
*6. I'm assuming here that Ennis's postcard - the one stamped "deceased" -
is returned to Ennis before Nov. 7
