Internal yolks

[powfinder13]

I had two Black Sexlink layers who in their third fall quit laying. both of these girls had been regular layers typical for the breed, However, one of them had always laid funky eggs - ridged, thin shells, double yolkers, etc. Anyhow, I hopefully waited 4-5 months but finally decided it was time for the stewpot for them. Today, upon butchering I found both of them had several yolks of various sizes inside, and one had a whole egg, shell and all.
What gives? Were they somehow gearing up to lay again? Were they just carrying these yolks around for months? I have no roosters, by the way.
Thanks!