I also make boards for a living.  In fact over $200 million
worth. You may want to think of xouts in a little different
way..if you build a lot of boards that are in the range
of 15x16 inches, there is a lot of circuitry and also there
is no room for xouts.  Therefore, you should learn how
to build large panels with a lot of circuits on it the same
way as  one large circuit and not allow the shop to build
them in such a manner as to require the customer to
accept bad circuits on  a panel.
In other words, you should be able to get a vendor of
PCB's to build perfect multiple up circuits on a panel
and not charge extra for that privilege.
However, it's not a bad idea to allow a 5% allowance
if you feel like Santa.  Murphy is alway lurking around.
regards..hg