Reminds me of a trip to Chiang Mai a few years ago - myself + 2 colleagues (incl my boss) on UA IAD-PEK, then Air China to CM.
Me & my co-worker were together, the boss ended up farther back...I remember as we walked down the hallway, at the turn towards immigration, the corridor wasn't really controlled and there was an opening. Maybe for people going thru to connect?
So we went thru the immigration line, and out to the baggage carousel...and the boss is standing there! We were surprised and asked, how did you get ahead of us?...he said I just walked right here. Did you get your passport stamped? No ...he had to walk back thru to immigration and get stamped.
I assume he would have been in for a rude surprise when he departed, had he not realized. We all know how Thai immi loves to hit people for violations