Where are Layout layer sets saved?

I created a number of custom layer sets in Layout XL but they aren't showing up anymore.

However, if I create another layer set with the same name as an old one, the name of the new one will have a "(2)" or "(3)" appended to it which indicates the originals are still saved somewhere.

Is there a way of loading the old sets or deleting them so I can recreate them without the appended numbers in the name?