Ah. I was thinking you were seeing them by candling. A lot of hairline fractures can be seen when candling but not with the naked eye.
They usually show up pretty well when you take a picture while candling the egg.
It sounds like your incubator temperature was a bit low. Coturnix quail normally hatch on day 17. I recommend putting a calibrated thermometer or three inside the incubator so you can see what the temperature actually is. Incubators lie.
The triangular break in the egg is indeed, a pip...