There is NO SUCH THING as a frozen ATPL. Not under JAA, not under FAA. The difference under JAA is that the higher level exams are accepted for the lower level license meaning you don't have to do them again to get your ATPL. The term "frozen ATPL" is rather stupid, frequently used by people to pretend they have something they haven't, and causes all kinds of confusion for noobs.
There is 1 exam per license under FAA regs. The exam, whilst covering the required syllabus, is more of a formality than anything else because it's the pre-checkride oral test which is really going to stretch you.