Originally Posted by
sama
If it was personal, itīs strange that they didnīt stamp it.
IIRC, agents in CDG (Paris) are known for not always placing an entry stamp in passports. It's quite possible that the same could occur at other locations with either entry or exit stamps.
Depending on ones trips, it's quite possible that one entered and exited the Schengen area multiple times on an individual trip. The Czech Republic, Slovakia, and Hungary weren't part of Schengen until 2007; Switzerland joined in 2009.