I rounded up all the "hidden" eggs yesterday to the tune of 28! I have about 24 layers with some more upcoming in Feb/March. This has been probably a few days for some hidden clutches and up to a week for one of them. Only about 7 seemed to be unfit for human consumption - not that I'm selling/giving any away right now - these are all ours or the dogs, especially since some have probably been frozen.
Some hidden areas are because they laid in newly spread straw in a corner that I can't see very well and behind doors that are hard to open/close due to frost/moisture so I neglected them thinking they weren't laying very many.