The lad who is annoyed that they can't cross reference the alternator to the pulley are you really that surprised? The alternator is bolted to the Engine block so should those part numbers cross reference?
Save yourself some time and money by registering on vagcat and just ringing them up
I'm on vagcat, however VW used 3 different make's of alternators (Bosch, Valeo and Hitachi) for my car on the production line, meaning 3 different pulley's. When looking at the alternator on vagcat it had no reference to which pulleys are for which alternator under my model of car, I eventually found it by searching vagcat and finding the same alternator used on another model with the pulley part numbers cross-referenced.
I just find it silly that the mighty VW can't cross reference the alternator part # with the pulley #, even AFTER giving them the alternator number which they said they would need to find out which is the correct pulley - thus lying to me.