From the SIG notes:

The only dispute - pairing 72 – is a long out-and-back that technically starts just before the “critical period.” If it were slightly later, it would be illegal for over 9 hrs of duty (MEM-COS-SLC-MEM).


So if the trip started later (shorter) it would be illegal. That makes no sense whatsover, even though he is correct. The letter of the law may be present but the intent (of the critical period) was raped and left for dead on the side of highway. If you need a better graphic, I can provide it for you.