I don't know what to tell you. I've only had chickens a couple of years so I don't know a lot. Do you have pictures of them? Maybe somebody lied to you and they're not leghorns.
Twice I have found large nests of eggs. Once there was 22 of them and once there was 17! The culprits were my SLW and black australorp. I just figured they weren't laying eggs every single day. I put a nest box out in the yard, this seems to have worked, I just put a fake egg in there and now if...