I've got six hens and the three white chickens that lay brown eggs have been going for about a month, but I don't seem to be getting anything from the other three black sex links that I got all at the same time from TSC. I have recently gotten a few eggs that seemed to be a slightly different shade and smaller, but still only seem to be getting 3 a day as best I can tell. It has gotten a little cooler here, so that might have gotten one of the white girls to not lay that day right??Mine have been laying about a month now. They still sing, but it seems to have gotten a lot shorter in duration. Perhaps there's a lot less "practicing" going on, and it only happens when there's an actual egg.
Might work the same for you as yours get older.. Or not.. Who knows