Quick upgrade / backup question

[peter@mxtoolbox.com]

I think I remember reading that Zimbra can only restore from backups generated by the version of ZCS which is running. Does this mean that every time we upgrade the system that the backups for the old version are unaccessible? I want to provide the latest version of Zimbra to my users, but I also get requests from time to time to roll an account back to a previous date. What's the scoop?

If this is the case, how do most people cope with this pickle? Any advice is appreciated.