The Cognac SCM

I'm using a file convention where when I'm creating a new version I rename the old one to <file>.o, then the next time to .vo, .xo, .xxo, and so on. When I have to rename 3 files, it gets too painful so I just delete the .xxxo one, so I don't have too many files around. For files I want to keep I include 's' (special) in the suffix, and when it becomes part of a point release '.vs' and sometimes '.vsop'. What do you think?