Instruments don't need to have just one Ab, there has been at least one that had more (as well as a rather uncommon B#): http://en.wikipedia.org/wiki/Archicemba

Instruments don't need to have just one Ab, there has been at least one that had more (as well as a rather uncommon B#): http://en.wikipedia.org/wiki/Archicembalo http://en.wikipedia.org/wiki/Archicembalo