So here is a strange question.... Because I Don't seem to be able to keep my hands Off the eggs...

It looks like I might have a quitter or two. Going on day 13 now but a few eggs (same hen) are hard to see into because of extra pigment and extra speckles. They have been hard to see from day one but at times I've seen obvious movement at times and though harder to see, some veins.
Now it's getting even harder to see and one looks not have progressed past day 9 maybe and I can't see veins anymore. I'm not going to remove them yet because I'm very unsure, but if they are indeed quitters at what point should I be concerned about an egg exploding?
(2 infertiles were removed and all other 20 eggs have had development and movement up until now)
Do the exploders tend to be eggs that never had development at all and just go icky then ickier whole time until about day 20 when they just pop?
It's happened plenty at the old farm when someone started laying in the rafters of the barn but did not actually set on the eggs...

.....but I know it also takes a little while.