Thank you for taking the time to look over the book. Hopefully others can also weigh-in.
The fraying of the to right corner cover is limited to the back cover only in that spot, not the interior pages. I have seen this before with books for this era.
There are several spine ticks with color breaks, I wish there were less. The light refractions makes some of those ticks appear to be color breaks.
There are also several bends that are hard to see in the images. Hopefully those will press out.
Could you please provide more info around your NG. What is leading this as a NG for you.
There is fraying/wear on the bottom right corner. I am not saying it was not trimmed as I am definitely not an expert on identify trimming. Could you please provide more details on your thoughts for the book being trimmed.
I do not see any visible color variation on the internal page edges. Books of this era tend to be miss aligned, miss wrapped and miss cut at the press and have other various production flaws. The corner looks very similar to several other CGC Blue and Yellow labels I have.