I won’t entertain tan or worse PQ on any age book.
Moderns only want WP
Late BA/Copper OWW OB
For BA/SA, I used to turn my nose up at COW or even OW.
Then I came to realize I actually cared more about the overall appearance of the book.
After all, they are slabbed, preserved, and the COW paper will last generations after I’m gone. I’m not even LOOKING at the pages of an actual slabbed book, just the FC/BC, so as long as it’s aesthetically pleasing to my eye, PQ is not as big a factor. I don’t mind saving the money either.