I exposed a sheet to a small exposure under my enlarger with no negative carrier, for about 1/15th of the time that I used for printing. My theory was that the spots might not show up if no exposure at all was given. I then put it in developer, and it developed to a light grey tone with several spots showing. I also noticed a dime-sized lighter blotch, and that the extreme edges of the paper was a darker tone, like a microscopic thickness black border, as if the brick of paper had been exposed to light and only the very edge edges were exposed, and the rest shielded by adjacent sheets. I can't provide a scan because I then blackened the sheet with a strobe because I find it useful to have black versions of all paper sizes. Probably this paper was mishandled at some point. I'm not sure how to make best use of it; I could cut it down and use it for contact sheets+proofs+test strips. I still find the spots a bit puzzling.