Would there be interest in having a "version" field for levels?
This would be plain-text, similar to the author / title fields. It wouldn't be displayed in game (at least the way I'm envisioning it - but I'm very open to displaying it if that's preferred), but would be saved in replay files - the intention being that it would enable authors to identify exactly which version of their level a replay was made for.
EDIT: Alternatively, it could be numeric and incremented by 1 every time the level is saved - maybe even including when undo history is saved. This could get really big quick, but presumably only a small number of versions would actually be distributed, so the author merely needs to keep a note of these (and not even that if using version control).