It may have changed to the A now? or the A goes to a B when ordered? I would go with the Dealer as they should? have the latest ETKA version with the updated part numbers e.t.c.
Kez, out of interest, are we talking about a genuine exchange vw/audi waterpumps or aftermarket versions? its just I personally have never seen or fitted a 20v turbo water pump fitted with metal impellors.
Regards,
Jochen.