Here is an example to never assume anything when incubating. I apparently wrote the wrong set date in my incubation book. I wrote that the eggs were set on January 22nd. They should have hatched last Wednesday but they didn't. I thought it was odd they hadn't filled the space when I candled on day 18. I put them in the hatcher and when they didn't hatch, I just left them because I had nothing else going in yet. I just went up to wingband some chicks and there was a chick out and 2 or 3 more pipping. I obviously got the date wrong.
I did something similar several years ago. I was doing eggtopsies. Eggs were about 3 days past due date so I took them to the compost pile to break them open. One had a live chick in it just about to hatch.
The moral is, never assume anything when incubating. We all make mistakes. Luckily I now have enough incubators I don't have to rush eggs out for new eggs.
I put yesterday's date in the book for the eggs I set yesterday. Or was that Saturday? Duh!