If you or your DC had a skin allergy test, how many allergens were you exposed to at one time?

DS got a test just a week ago and was exposed to 8, I think that's customary but SIL thinks a doctor should test for at least 16 allergens to be more thorough.

DS didn't get a reaction from any of the 8 but we know he's allergic to something...

Should I go back to the doctor and ask him to perform another test?