Here is my experience from a newbie with 34 logged contacts, 16 confirmed.
I've received a couple of QSL cards (e and paper) that I didn't have any log entries for or my log data was different. I record, or at least try to, all my contacts and save the recordings as an .mp3 file. In the cases above, I have attempted to email the sender and explain the discrepancy and ask if they have an audio recording they could send in the case of it not being in my log. If it is a data discrepancy I explain that and ask that they double check their log. In one case the sender replied that he had indeed listed the wrong satellite and would send me a new card.
I've also been on the other side. Last April my HD crashed, I lost my logbook and I was unable to find any backup. Getting involved in other things, I was "off the air" until this February when I happened across a backup of my logbook in an old CD-R I was searching. I noticed that there were some contacts I hadn't sent QSLs for nor received. I sent the QSLs along with a note explaining the delay. Reading some of the responses I now understand why I haven't received any replies <grin>. I did receive one card returned explaining that the QSO was not in the log.
In the past, I have trimmed my recordings to only the time I make contact. What I think I'm going to do now is also save the raw recording for a couple of months incase I need to verify a questionable QSL either sent or received.
73, Kent K5KNT AMSAT #36765 ARRL Sent from: San angelo TX United States.