When I was with Qatar I was trained on the A300-600 (of which we had several different configurations and galley layouts which was very confusing), A330's (all basically the same so it was not too bad) and the A319,320,321 all of which differed slightly. Now the doors on the A300's and A330's were very similar but the internal configs and locations of equipment varied so much that it would be impossible to be sure exactly where everything was.
Now in BA I am trained on the 747-400 (2 types of basic configs with a few other variations depending on which aircraft you are on on the day), B777 with 4 basic different configs and galley layouts and finally the 767 which fortunately are all the same but are so different from the rest of the fleet right down to the doors.