Yep, possession is establish by completing the "process of the catch"... which shows you have established possession.
In the case of the runner, he got the ball, and made a football move before ever breaking the plane. His need to establish possession has already been taken care of.
In the case of the Calvin catch, they blew it. He caught the ball. He clearly established possession. He went to the ground with possession. He dropped the ball while getting up.
That's not the rule. You don't have to hold on to it while getting off the turf, and Hochuli knows it to this day.