This is an all to common situation in a lot of dealers now.
Many if not all are not allowed to order an replacement parts, without the direct authorisation from the manufacturer first when dealing with a warranty claim.
This can necessitate two visits in a lot of cases, which can be seen by some as counter productive.
One visit to investigate the problem, which MAY involve some investigation work like removing the door card etc.
Then a second visit, to remove the door card again to fit the new door lock !.
This was the same in my brothers case, one visit to investigate and another one to rectify the issue.
Maybe they DID have a replacement lock when you called, but that found its way onto another car.