[Sorry to disagree, tpe, it seems to me that the last meeting took place in may 81 (just before the promised august) and the visit at Lightning Flat went immediatly after (Jack told Ennis of his purpose)...
Time line is a "goddamn b** of a unsatisfactory thing" in the screenplay, so we may have not to bother about it.
Jack did not spent 4 years with that shadow of Randall. We must keep to the film, and the film only: remember what we see, the face of Jack, full of sadness, Jack is dying without Ennis! Immediatly after that is the last camp and that is what matter. The path of time is not realistic in this movie! Jack is trying to hook Ennis and Ennis is so proud to talk about Cassie "look, I'm no queer" So Jack tell him what he want to hear "look, me neither" and immediatly after the TRUTH, sometimes, I miss you so bad... Randall has nothing to do with that. Who speaks of Randall, that is John Twist who is pure hatred and he does it to wound Ennis, he tried to destroy!
Mélanos, there is a thread where this entire problem has been discussed with some hand-wringing!

The screenplay says that Jack's death occured in 1982 and that the last meeting in 1981. If Jack died in 1982, then the projected November meeting could not have been in November of 1981. The projected meeting will then be November of 1982.
Since snow was mentioned in the last meeting, there are only 2 possibilities:
1. spring of 1981
2. fall of 1981
If the projected meeting is set for November of 1982, then fall of 1981 would be the most likely and reasonable date for the last meeting. This still gives a WHOLE YEAR between the last meeting and the projected meeting...
I also believe that Jack tried to keep his affair with Randall in check -- perhaps even trying to avoid it for most of the intervening years.
And yes, the dates are problematic. But we can arrive at one reasonable scenario for the screenplay dates, and this is discussed in the thread dealing with the timeline of the last scenes.
I throw up my hands in despair!