SA Apparrent Small amount of black pen color touch; easy to detect?

[Noble Nostalgia aka Nikelspot]

I recently bought a raw higher grade early silver age dc key from a person that bought it from a reputable dealer. The book came back 8.0 SA small amount of color touch on spine done with a black ink pen. I held the book in light and didn't really think to examine the spine because the black on the rest of the book looked fine The guy I bought it from did not state that it was restored. When I contacted him about he said that he bought it from the reputable dealer and has had four dealers look at it. He just informed who the dealer was that he bought it from and the book had a label on it that stated vf/nm with no restoration mentioned. Is black ink pen easy to detect on books? I know if the size of the restored area is tiny it can be difficult, but pen will have a distinct texture and a red or silver hue.

[Hero Restoration]

It seems to depend on the marker and if it overlaps ink. Markers that have a hue seem to bleed less while markers that don't have a hue bleed easily.