[CentOS] Fix passwd/shadow/group files?

I've been copying old passwd/shadow/group files from system to system for ages across different distributions/updates and would like to get them back in sync with each other so the system tools will work. Now they hang like:

#userdel irose hangs forever, syslog says: Jul 12 11:19:32 newftp userdel[30335]: delete user `irose' Jul 12 11:19:32 newftp userdel[30335]: delete `irose' from group `ftp' Jul 12 11:20:02 newftp last message repeated 373404 times Jul 12 11:21:04 newftp last message repeated 646597 times Jul 12 11:21:06 newftp last message repeated 29123 times

Is there some kind of test/diagnostic tool I can use to clean up the parts that don't match anymore? Preferably one that doesn't hang forever when something is missing....