Printing Error (?) 4c Taft (Scott 685?)

At the beginning I decided that this stamp is just dirty, but...the "dirtiness" doesn't cover the entire stamp.
So, I really need your comments and help!
Am I right that is Scott 685?
What do you see, how would you describe that, is it printing error, etc.?

Looks like it was printed on both sides. I've never seen one so....my opinion is not in any way expert.

685 - Not printed both sides (image is reversed so it can not be); whatever funk is on stamp simply bled through. It is a badly damaged stamp(s) from some kind of funk (glue? tape residue? some other old adhesive?) The odd part is that it appears to follow the outline of the printed image but its anyone's guess what this stamp ran into. Whatever the containment was it appears to have been attracted to, and soaked into, the inked parts of the stamp.
Don

the back is with an original old gum. As for me it looks like the printing was very oily, so, gum just increases the contrast on the back.

The front has a box cancel. It is possible it retains the original gum but other 'things' might have also happened to this stamp.

If you keep it you might want to make sure whatever this is does not migrate to the album page or other stamps.

Thank you, StudeBaker! Thank you all.
Does it worth to be certified?
I made a few pics (photocamera reflects softher color but may show something that was not obvious in the scans).

Aurora, there is really nothing to certify here except maybe what kind of agent the stamp was exposed to (through a chemical analysis of the paper, maybe). Not worth pursuing, in my opinion, but I think it is a great curiosity piece. I've never seen anything like it.

Thank you, Duddley.
As it was sold and used, it cannot be named as a printing waste. It is unique! )) I love it.

I do not think that anything happened to this stamp when it was printed. I see no shifting of the design or any evidence it was printed more than once. Something bad (solvent?) soaked into stamp/ink; most likely after it was in the field.

Ugh, I looked at it and specifically thought, the image is oriented correctly so it's printed on both sides... and the forum replied, "Doofus"! again.

I have seen this problem on quite a few stamps over the years. It is oil stained, with a light weight oil that has soaked into the paper. You can get staining like this from a deposit of grease too, but that usually has some heavy stuff nearby. How it got there is anybody's guess, but I would not be surprised if it spent some time on a floor. The "donut" shape has to do with the object it contacted to get the oil, including freshly lubed mail handling equipment.

I would mount it backward in my collection. Pretty neat!

Thank you all for your comments and suggestions!
I really appreciate that.

I have seen similar damage when stamps were kept in Polypropylene PVC
Coin Pockets Sucks the life out of stamps.

Thank you, Rod2222.
It was kept for a while hinged in a very clean/dry and accurately organized album - all the paper pages separated with clear plastic pages. No more stamp is "damaged" like this one (especially the stamps that were sitting on the same page).

It was probably damaged by a prior owner.
Kind of a neat, dramatic example to promote a 'take care of your stamps' campaign.