The fertility could have been decreased because during the summer months the males tend to stop mating with the females because it is so warm. Or it could be rough handling by the post office or they might have gotten x-rayed.
I've had a few dozen guinea eggs that never developed. All had loose air cells, so someone at the post played soccer with them. Go figure.
Shipped eggs have a 50/50 shot of getting anything usable. Sorry
Dont know if it was the post office or who knows what But I bought some eggs off BYC and none turned out
and I bought some off ebay around the same time last month had 5 out of 7 hatched.
I'm on my 2nd ebay bought eggs day 18 bought 6 and 5 have chicks in them,