For every person that says they hatched on 21 days there's someone that says theirs hatched day 18-19. That's why I'm going just one day early. If they do hatch on day 21 stopping on day 17 won't cause any harm. I've been forced to do it before with other hatches and those were some of my best hatch rates from shipped eggs. If they do hatch on day 19 raising humidity on day 17 may prevent large losses. I've read the first hand accounts, I've seen what the breeders and sellers of the eggs put down, and I made my decision to stop turning on day 17 whether they hatch early or not.
All I can think of with the chick is it died sooner than I thought and the blood did not drain from the vessels around the membrane for some reason. It still is no younger than 14days though.