Getting in on this thread late but..
When I got my '90 Westy almost nine years ago the gas cap locked with the
ignition key.  Still does for that matter.  And I know a bunch of others
with the same setup.  Yet John got his '91 new but different gas cap key?
So what the heck was VW doing about that time? Flipping a coin between
Vanagons to see what van got what?  I'd always assumed that stock was with
the ignition key for the gas cap.