Further information re
tacking count for loaded transports comes from the July 2009 Unofficial Players Guide for PG 3rd ed.This document was updated around every 4-6 months before the advent of PGHQ and its annotated rules.
Answers and rules clarifications were only added to this document once AP's current 'developer' had been consulted. Therefore the answermay be from Doug McNair, MB or whichever 'guru' was in situ at the time. It says
"STACKING"
"4.1 You CAN (their caps not mine) have 3 loaded transport/APC and 3 combat units all in one hex. The penalty for forced unloading (5.66) that results in over stacking is elimination of the over stacked units, chosen by opponent at end of turn"