What Does Yellowed Gum Mean?

I have a mint copy of U.S. 231 (2 cent Columbian). From the front, it's the best appearing stamp in my collection. Balanced jumbo margins. It even has selvedge at top with the plate number and American Bank. So far so good. On the gum side there is what appears to me to be never hinged gum (I consider myself to be an intermediate collector at best). There is however what appears to be some light yellow staining in the lower right corner of the reverse. I'm thinking the gum may have been sweated, or perhaps the stamp was stuck to something at one time that imparted the stain. Am I overlooking something? Before you ask, I'm inept when it comes to posting pictures to this forum (if it was Facebook, I could do it). I'm thinking maybe I should submit it to PSE or PF for a cert, but even they aren't going to provide an explanation.

Really need a scan. Why certify this damaged/faulty stamp?

Certification will cost something like $30 plus return by registered mail charged to you. Not worth it here, in my opinion.

It's impossible to tell what's gone on here without looking. With Columbians and other issues of the period, the paper holds the embossing done when the stamp was printed. The gum should be then evenly applied over the hills and valleys, not piled up in the valleys or flat surfaced (and thick). Gumming wasn't perfect then so there can be ungummed skips. Stamps with gum skips and no hinging are NH, but no NH collector today would count that as NH nor would anyone semi-knowledgeable pay a NH price for it.

Staining is staining; stuff happens and is rarely due to someone manipulating the gum.

What are you doing about that? It seems to me it would be to your advantage to get good at it. Especially since I know it is not difficult learning how to work with the tools here. I am in full reply mode, and there is a link to the image tutorial just below the box where I am entering text now.

Here's the link for the tutorial:
https://www.stampcommunity.org/sc_t...g_images.asp

Read through the whole thing before trying to DO anything.
You can do this, and we can assist.

essays, that would require a modicum of effort on my part.