Great list and thoughts. What about educational mindset as a factor?
I watched a presentation with Jeff Meldrum on YouTube.
Essentially, he said the school of thought in the 1960's was man and apes development would be linear. That is, science followed the idea mankind went from A-Z under one linear path to get from primitive man to now. Nearly everyone adopted this until post 1960's (Lucy) discoveries re-wrote the theory. After that, science was more open to multiple paths toward mankind. (this is my take on what Meldrum said but it is not my area).
Meldrum emphasized science in the 1960's era essentially required the complete rejection there could even be something like Patty. Science view was essentially this (my paraphrasing): "if today there was some primitive ape to appear it would have to mean it was a hoax" based on the accepted parameters of the A-Z thinking. He mentioned this explained why those who looked at the PGF in the 1967 era were- as a group- largely still in the A-Z camp. This required they rejected ahead of time the even the possibility the PGF and Patty could be real.
As you outline the steps in determine credibility, we need to take into consideration pre-emptive Educational Mindset. In the case of the 1960's, this led to a near certainty the PGF would be rejected.
Great videos, witnesses, and so on might not be a match to the closed mind.