[Forever Young]

Psa is better than anyone in determining if it is a type 1 or not as it is their system. Every other authentication company copied the system in one way or another and their research.
That said, everyone makes mistakes. So do your own research.
A Psa type 1 letter is a wonderful start if you are going to buy a 10k photo but also know why it was classified as such. It is a good way to preserve your investment t as well.
There is a lot of regurgitation in this thread so be sure to ask the right people the right questions and you will be good.
You seem to be doing well this far.

*edited*
Authentication and grading are separate things obviously.
1) is it an authentic type 1?
2) what would it grade?

Drc(very knowledgable and has written books/trailblazer in the photo hobby) is right in that Psa got is right. They don't numeric grade photos for many of the reasons stated in this thread(and probably will never).

Mark(also very knowledgable) doesn't care about the condition is much as many others. I can say that I also do not need a "mint" photo but certainly would like a nicer example if available.

Rmy/Rhys(hi) is also very knowledgeable. He would be a good contact as you know. He applies a grade but only as a guide obviously(I believe). These are not baseball cards. There is no way to grade these across the board/consistantly unless you grade them as such.

These are photos.. Works of art. I would rather have a complete Mona Lisa than one not whole or damaged. That said. If there is an iconic image and there is only one example available or if a higher example would run 50 times more, I might buy it. They were used and a little wear is expected.
Everyone has their own tolerance and price points. Buying a lower conditioned photo does not mean one has bad taste just like someone paying a premium for a mint example doesn't make them an ego maniac.
If everything was equal, one would be a complete fool not to take a nicer specimen.