Back in 2001 I had been diving for nearly 40 years but was frequently asked by instructors from some agencies to do a "check out" dive because they didn't recognize the level of training involved in my agency's "OW" course. While on the Great Barrier Reef, I encountered a PADI instructor who not only recognized my agency and its training, but referred to my 1960s c-card as a "museum piece." I took PADI's AOW course with him for just the cost of the materials. It made next to no difference in my diving skills (although I did learn a few things) but now none of the other agencies questioned my skills level. Sheeez.
Back when you were first learning to dive (1967, IIRC), another diver ran into a similar problem in Australia. He had gone there for a week of intense diving off of a boat. The captain asked for his C-card. He didn't have one. He explained that his father had taught him to dive, starting when he was only 7 years old, and he had completed thousands of dives since then. The captain was not impressed. No card--no diving. He could hang out on the boat for the week while everyone else dived, but he could not go in the water. Several crew members met with the captain and begged him to make an exception for this one case, and the captain relented. As soon as the diver got back home, he went to the local PADI shop and got certified so he would never have to go through that again.
His name was Jean-Michel Cousteau.
I am pretty sure that this diver, the second human in history to dive on that new-fangled SCUBA device, learned nothing during his certification class, but he recognized that it was something he had to do.