That was a good move for you. I just returned from two days' drive and I want to sleep for a day or so now. . . .
36...a5
Playing this kind of conservative. Lots of moving parts.
37...Rg8
38...Rc8
39...axb4
Pretty much obligatory, and expected.
To add some running commentary I guess.
I considered taking the pawn back with my bishop but, not to give away too much strategy, I like the constraining effect of the bishop on that square. That combined with the pawn structure makes moving the major pieces (in this case king and rook) difficult.
taking my b4 pawn with your bishop was, I think, your best move. It would have been almost "counter-intuitive" to do so, though, I realize. When I looked at the downstream moves ensuing, it would have been a pretty wild ride, so your preference for having a "constraining" effect keeping the bishop where it is, is pretty true. It's a matter of style I suppose. I'm the more flamboyant sort and more inclined to do stuff that is "counter-intuitive", or reckless perhaps, but playing you and others in here has forced me to lay off that style pretty much. Too hard to recover from a bad move with you-all. . . . . .
The next question. . . . well, it's huge.
40...Rc5
41. Ke4
41...Ke6
OK, so maybe you have a different board somehow, according to mine, your move Ke6 would be excluded by my pawn on d5. Did you mean Ke7? Would our difference in board positions have altered your moves since the last pic?