AMO bow length describes the correct AMO string length, not necessarily the physical length of the bow (although that was true pre-AMO). Makes sense if you think about it; you can't do much about the bow length, it is what it is.
"The AMO prefix to bow lengths in inches means that the bow has been manufactured
to a length that properly uses a bow string designated with the identical
AMO marking. (i.e. A bow marked “AMO 60”, 50 lb. will brace to the proper
string height with a string marked “AMO 60”, 45 lb. to 55 lb.)"