1991 Pro Set Football Forum

I think there is a variation missing from the database. There is one where the NFLPA logo is very faint. Comc regognizes it: https://www.comc.com/Cards/Football/1991/Pro_Set_-_Base/83/Jim_Kelly_(Slight_ghost_image_of_NFLPA_logo)/11324298

We don't list printing glitches. If you'll notice who the seller is on that card, Junk Wax Gems.  He has a blog about everything he considers errors; I emphasize "HE".

"He" is very clear in making distinctions between errors/variations and RPDs (recurring print defects), which are all added to master set checklists while miscuts, short run print flaws (fish eyes), printer's scrap are not.

RPDs are print flaws that affect a significant portion of the print run. This is a very collected aspect of vintage Topps master sets and legitimized by most collectors seeking to build master sets. 

In the case of the Jim Kelly card listed here, it is 100% a true RPD for thata set. It is actually fairly common for both Kelly and Slaughter's cards to have a portion of the NFLPA logo still present. Not a one-off or freak misprint at all. Whether it makes your master set is up to you.

Your subject line does not say "RPD", it says "variation".  It is well established that listable variations require there to have been different printing plates making each of the versions (unless the variation is in the card stock itself).

-Tom

It is not my topic/post here but I have put more time and research into this product (and 1990 NFL/NHL) than most and what the OP is mentioning is not a "one-off" or print flaw. It is a recurring print flaw that could qualify as a variation. A significant portion of the run, specifically, a transitional printing, has the faint or trace NFLPA logo still visible. There are two other cards in the set from this same transitional printing that have the same issue. If you know Pro Set well and are familiar with their production history, they were very open about going back to press and making adjustments throughout their production seasons. In some cases, they did as many as six different print runs and some of the changes they took effort to make would seem like insignificant print flaws to anyone not interested in their products.