Agree with both you and mrsnork. When I had a 100% print for a month, and my wife now still 100% over 2 months, that was with only one thumb registered.
I did have something go way out of whack very early on, documented in another thread, reported it to Apple and was given a data capture profile to gather logs on TID, but could not duplicated the problem. I left it with the tech that there was something lurking. It reassigned a print to a totally different finger as far as names go after deleting a newly added finger. The old finger failed 100%, yet the newly added finger, deleted after adding it without leaving the "add a fingerprint" screen, still worked, only under the entry of a different finger. It was very strange, but not repeatable.
Starting to think something is hosing pointers into the database, and the multiple entrys are being corrupt over time...
Might be worth a shot for those still having failures to try deleting all fingerprints and redo just one using the method I posted in this thread.
If this produces better results, this is feedback which would help Apple pinpoint the problem, FWIW.