Odd stuff on finish

I just unpacked some of my older built-ups after a move to discover something odd. On my built-ups that are painted light colors (like white or light grays) and are sealed with Dullcote, there are small black spots. They are about the size of ground pepper or maybe periods from a newspaper.

What the heck are these things and what can I do about them, if anything? They almost look as if they are in-between the overcoat and the color coat. They are all over them, not just where there are decals. I have also noticed that the same kits have a faint yellow tinge to them, as if the Dullcote is turning colors like old floor wax of something. Wierd. Does Dullcote turn yellowish over time? (Like decades, we're talking about here...)

I moved from SW Missouri to Southern West Virginia, so it's not like we were in the tropics!

I haven't tried removing the spots yet, pending any ideas from people on what they might be and what might be done about them. Suggestions and ideas welcome. I figure that I have nothing to lose by trying, at this point.

Gregg