there are conditional value lists in FileMaker
check this out (among others - google..) Creating conditional Value Lists | FileMaker
I'm on iPad, therefore I can't show an example - but it's one method to deal with that. The value-lists should be entries in a separate table - as You mentioned
There is someone very active on the Forum, PhilModJunk.
Visit his website (Caulkins consulting) and you will find a lot of examples of conditional value lists. (You can download them for free).