Blastoderms or not?

[athena's chickens]

When we got our (4) chickens they told us they were all female, yet these eggs they've layed look fertilized? I'm just noticing the "blastoderm" now, I hadn't seen it before in any of their eggs. Three of them have been laying for about a month, one is not laying. I didn't think any of them were roosters, what do you think?

 

[JaeG]

This popped up about a week ago with someone else. Here's the thread so you can have a read. Apparently this happens but the eggs won't develop if incubated.
https://www.backyardchickens.com/threads/fertilised-egg-no-rooster.1221383/