You report playability issues, and we address them when we work on the upcoming builds. When people fail to report problems, or they discover something that is obviously unintended and exploit it, that is what causes incompatibility issues in future versions. We are trying to address most of these for 2.53 and 2.54, but no-one is bothering to take the time to work with us on that subject, so if it is not important to the users, then we are not going to overly worry about it.
My comment was a quasi-trollish way of saying that, if people have enough time to discuss something this esoteric (and inherently non-quantifiable) at length, then they probably have an hour or ten to kill testing their quests and reporting problems.
2.10 tuff should all be fine, as far as I am aware. 1.92bXXX is where ZC begins to take it in the arse, because there were so many changes in 1.92 that were never documented, and we do not have the 1.92 sources at all (nor the 1.80, 1.84, and 1.90 sources). I do have all of the 2.10 stuff, though.
Stuff though, like precision timing on how many i-frames a leever that is descending into the ground has, should probably not be a merit-worthy thing around which to base a game mechanic. There is also a required decorum when presenting these cases to us, for inclusion (support), as it basically requires us to implement, and to maintain an engine hack for one specific case at a time.
In general, I try not to implement any changes without a rule or version-based exception, but nothing is fool-proof. I think that 2.53 has the greatest compatibility across old versions of any recent ZC build (2.10 or newer). If you know where there are copies of the 1.92 sources, then we could probably use that to add greater compatibility, later; but when we patch stuff now, we generally need to do it by observing the old behaviour and emulating it. Given that we cant run 1.80->1.92 on modern systems, that is a rather large problem with no ideal solution.