I once read leave the eggs in you car glove box and in 60 days you`ll have babies. This is an extreme but a good example I think. I show eggs to my friends, relatives, etc a lot. Opening the tub every time, candling them, nothing happens. In nature they get colder days, hotter days, rain, etc.

First if the egg looks good but there`s no veins dont even put it in the incubator.

My opinion is this, and its just my opinion. You say the went bad almost full term, that`s when the babies require more air. Maybe opening just once a week wasnt enough. I dont like to use press n seal, and I do two air holes in the egg tub because I want air flowing. I dont think it has something to do with genetics or bad temp during follicle growing, issues would have shown earlier. Again that`s my opinion.

Good luck, dont give up, and relax, its easy.