I'd like to suggest adding an optional version field to the level format. This information, if present in a level, would also be saved into replays made for that level.
The main use of this, in my opinion, would be for replay management. Currently, other than trying to load it and see if it works, there's no way to tell what version of a level was made from unless it's been baked into the filename. You could alter the level ID, but then a replay is recognized as being for a completely different level, and depending on what changes were made, there is a chance the replay might still pass - so it is still potentially useful to load a replay from an old version in a later version of the level - certainly, the chance the replay passes is a lot higher than the chance a replay from a completely different level passes. I believe you can still load the replay anyway, but it would be useful to have a different warning for "This replay is for a completely different level" and "This replay is for a different version of this level."
Sometimes, people have an outdated version of your level (and don't realize it) and they submit a replay they think may be a backroute. It may still be useful to watch the replay, even if it fails the current version of the level: is it an old backroute that you've already fixed? Or is it a new backroute that could still be made to work in the current version even if the changes to the level were enough to break the replay? But which old version of the level does the replay go with?
If a replay from an old version passes a new version, it might be beneficial to have it automatically resaved with the new version as well, either as a separate file, or by allowing the replay to store a list of versions that it's known to work against.
There could also be some potential for discussion of what, if anything, the editor should do to help manage this, but I think that might be best saved for after we decide whether or not this feature should be added at all.