Read this from the egg quality handbook.
https://www.thepoultrysite.com/publications/egg-quality-handbook/28/blood-spots
This has nothing to do with a roster or fertilization. The yolk starts out as a tiny ova. It grows surrounded by a membrane full of blood vessels carrying nutrients to that growing yolk. When that yolk is big enough to become a yolk in an egg, that membrane splits to release the yolk to start its journey through the hen's internal egg making factory. It is supposed to split along a line that has no blood vessels, but occasionally a hen has a glitch. One or more blood vessels wind up breaking, so you get blood as well as yolk on that internal journey.
Some hens are more prone to this than others but if you follow that link you'll se that it is not that uncommon. The Egg Quality Handbook is mostly written for commercial flocks but we can learn a lot from it.
These eggs are safe to eat but there is a YUK! factor that many can't overcome. The commercial operations candle their eggs before they go in the carton for people to buy, they don't want their customers to get that surprise any more than you do. They don't throw those eggs away though, they sell them to places that use them after they are broken, maybe a bakery or a pet food factory.
The egg quality handbook talks about meat spots too. A bit of something breaks off inside the hen's body cavity ad it enters that egg making factory and winds up in an egg. That haooens inside your body cavity too and your body reabsorbs it. Again, they are safe to eat but there is a Yuk! Factor.
None of this is strange or unusual, it happens all the time. You are just learning more about what real chickens are like. As long as your hens are acting normal, there is nothing wrong with them.
I might as well include this link if you want to see how an egg is made.