You never know how the PO handles them, but that being said they are just a total enigma IMO, lol.
I have shipped birds across the U.S. and there have been great hatches.
I have carried eggs from my pens 100 feet to the incubator and had terrible hatches.
Sometimes I cant contain myself and candle a LOT and have great hatches, sometimes I never candle until the end and have bad ones.
OR vice versa.
Some hatch on 19 and some on 21. Think it has a lot to do with temps.
Some stop developing after 10 days and some stop when they should pip.
I have yet to figure out the secrets of the incubator with serama eggs .
Here is the only secret that I have to offer:
Silkie cochin cross super broodies!! lol
Nearly 100% every time!
Sometimes I have a broody hen sit on eggs for 10 days, then I take them and put them in the incubator and give her more eggs.
I do this 2 or 3 times so she only sits for 20ish days and then I break her up
----- or let her hatch the 2nd batch if she is eating and drinking and keeping weight.
Much better hatch rates!