Actually,
@Tiana's chickens , other than one seeming a bit iffy in appearance, they don't appear fertile. They have a normal white spot on the egg. Even after many years of doing this, some are not clear to me, either, just takes experience to guess at the ones that are not really clear. If you have no rooster, obviously, they are not fertile.
Some blastodiscs are small, some are larger, not all are identical. Some are just a tiny spot, some have less defined edges, but I don't see a true bullseye on any you showed.