Yes if a mechanical fuel pump air diaphragm hardens you can see an increase in pressure. Doing some of the test recommended would help you isolate. Pressure test, inspect the needle and seat. Something changed from the layover. Since you changed carb it may be fuel system pressure. But a sitting carb even if running previously can have the same issues. So unless you move a carb from a running car directly, you might not be able to cross it off the list.

By the way, even with a non vented gas cap, aren't gas tanks vented twice anyway? Once from rear and one from front via the overflows?