But they did a good job of it? The change of behavior is San Andreas is due to an invalid memory access reading out of bounds into an area of the stack that was only coincidentally initialized by a previous iteration.

They didn't make any changes in correctness. The game itself is broken, and it's normal to undefined behavior from out of bounds accesses will change between OS versions, even just for security reasons. In fact, other versions of the game did fix this bug in a patch, it just didn't get picked because people go out of their way to downgrade the game in order to maintain some cut assets and features.