Hi Shadow —
If you would like to use some of those problems from 72-81 for your drill assignments, I suggest you utilize one of the study schedules (either the 4 week, 8 week, or one of the 12 week options available here) that are designed for use with just prep tests 72-81 — these will automatically assign some problems from 72-76 into your drill sets for you.
If you are utilizing one of the study schedules that are designed for use with 62-81, they will automatically assign 72-81 as full exams.
I hope that helps — if I misunderstood your question or you need anything further, please let me know! —
Mike