Replaced both these (one for the AC) on my E39 just over a year ago with Bosch ones bought from Eurocarparts.
Had to have the waterpump changed at my local specialist who I've found to be scrupulously honest. And they said both needed changing.
The smaller AC one had a split at exactly a right angle if you folded it. The longer one was cracked and breaking up on the ribbed face.
The originals did some 5 years and 60,000 miles and I changed them just as a precaution, and the larger one was in better condition than this one was now. The AC one looked a bit crusty on the outside - cracks etc - which is why I changed them.
Worth pursuing? There is a code printed on the belts. Would this give date of manufacture? I'll have the receipt somewhere.