Timing Belt Audi AAT: Old vs. New Differences

Hi there.
I've noticed that there was a change in part numbers for the timing belt drive on the Audi AAT (5-cylinder TDI) engine.
Early AAT models, up to around 1996, have a timing belt with 124 teeth, while later models have only 122 teeth. Also, the part numbers for components like the water pump and tensioner pulley have been changed.
What are the differences between the "old" timing belt drive and the new one?

Regards,
Jens.

Early models, produced up to 1994, have a fixed tensioner, while later models have an automatic one.