You can don a latex glove and insert your finger into the vent, if they are laying you should feel the shape and hardness of an egg if they are laying every day. Even if they have layed earlier, there should be one more in the shute, so to speak.
Each chicken has their own hormonal rhythms and can molt at different times.
About free ranging....mine free range sunup to sundown on some very rich forage, but they still eat their feed and still lay, so I don't think it could be free ranging.
I don't remember if you had mentioned or not, but have you looked for outside nests? They are very clever with their hidey holes and hidden nests, I've found. It seems when one starts this, they all want to lay in that nest, so its like an insurrection! I found a nest from last year that had 16 eggs in it....all rotten to the core!
Also...check for black snakes robbing your nests. Very slick and can eat quite a few eggs. So can rats.