This is very interesting: in
QRP Basics by George Dobbs, G3RJV, Founder and Hon. Sec. of the G QRP Club, I'm reading that
the 72 greeting was first used by Oleg Borodin, RV3GM at the end of the 1980s and has caught on as a greeting between QRP stations.
So we have the inventor of the 72 greeting on our ship and you, Fred, can ask to him directly.