Hello Matthias.
We are sorry but we have no access to the records of a certain garage.
We are no official institution or supervisory body.
I suggest you contact "Auto Technik" directly.
But - even if it is true that the belt has been changed in 2003, - it is 6 years old now, and that is quite old! So I would change the v-belt (Keilriemen) anyways.
with kind regards
Blecky