What are these discoloration spots on ceiling around screw heads?!?

[Billbill84]

Hi guys,
Back again with another question. Ever since we lived here for last 2 yrs I noticed these strange stains or discoloration marks on the basement ceiling drywall. I've monitored for over a year and nothing's changed or gotten worse. Good thing is is that it's not even noticeable, but it bothers me lol.
At first I was worried there might be a leak from the bathroom just above but the only discoloration I see is only around the drywall screws so that kinda throws me off. The stains total of 4 are slightly different in size by a few inches and all in the same area within 14" apart.
I was thinking that if it was leaking above the stains wouldn't just be around screw heads. Could the screws themselves be the cause?
Only other thing I could think of is that maybe the last owner tried to cover some "popped" screw heads and mismatched the paint?
Idk, thoughts?

 

[Snoonyb]

Prime with an oil based transitional primer, paint to match and forget-about-it.

 

[Sparky617]

Several are nail or screw pops where the drywall compound has separated from the head of the nail or screw, usually due to movement in the drywall. In this case, remove the loose drywall compound. Drive another drywall screw about an inch away from the popped one on both sides of the pop. You should probably sink the popped screw/nail a bit deeper. Then apply 2 coats of drywall compound, lightly sand, prime, and paint.