Are you 100% sure they were fertile? Are they fresh eggs? If you come up this way and want to bring some for me to try I will, or have someone else try. If they succeed then you'll know it's you. If not then you'll know it's your birds.
Any chance they are related? Where did you get your birds? Fertility/hatchability can be a problem with show lines.
They were definitely fertile, definitely have the little bullseye mark on the yolks. So just say I had an egg from the 10th, 11th, and 13th I cracked open the one from the 10th, saw the fertile mark and placed the last two in the bator. I haven't gotten an egg from my Silkie hen since. These eggs are from my lavender hen and lavender roo from Geri Godina.