Hi, please see what appears to be a ‘D’ across from Lincoln’s nose. Thoughts on whether this could be a misplaced Mint mark? I know you prefer not to have photos of images from a microscope but added one here because the spot is so small it’s hard to show it from regular camera photo.
That's a plating blister on a copper plated zinc planchet. Not a mint mark. Your 1991 was minted in Philadelphia with no mint mark. It looks like a D because it's considered Pareidolia. That's when something looks like something familiar when it actually isn't. Also.. A true D mint mark looks like this. Same size as the numbers and more pronounced. 2019 cent used as reference.. But hey. You have a misaligned die strike on the obverse. Slight but nothing major.
The mint tech would have had to be at the wrong place at the wrong time and drunk out of his mind. LOL. What @paddyman98 said ^^^