What is the average egg laying cycle?

Most people that have hens for eggs(not pets) cull or sell the layers at about 2 years, because of the lack of production.

I have heard this as well. Hens that are bred for egg laying just don't last that long. I find it somewhat suspicious that they would all stop at the same time though? Have you tried putting a light in the coop? I believe that is supposed to help with egg production. Hope this helps.

Keep in mind, that more than one story has unfolded on this forum, of hens that age that suddenly had their egg production drop, where a huge stash of eggs was found out in the yard.  Even with people that had already looked for a stash.  You could try keeping them in temporarily and seeing if you suddenly get eggs.  Do you have a run for them?

Chickens usually have more of a tendency to gradually slow down in their laying, not go full tilt and then all of a sudden just stop, due to age.

Things like being broody, heavy molting or the shorter days of winter, can stop laying suddenly.

We aren't using any supplemental lighting right now, some of our chickens are still molting and we are still getting eggs from grown hens.  So, I'm really wondering if they aren't just laying out on the property somewhere.

Sorry, I didn't see the part about them being rangers. I would also say they are probably hiding their eggs somewhere. I have about 8 hens that should be laying, no wait that would be 9. I only get 2 eggs a day because they do hide them. I find them occassionally, with a nest of 12 or more eggs, take the eggs and they move it somewhere else.

You forgot 3 more things.... sickness, stress, and Nutrients these can slowly reduce laying and also bring it to fast stop.  I would say its just a molt or hiding eggs though.

Chickens only lay well for about 18 months to 2 years.  It's fall too, and the lack of 14 hours of light will stop them from laying too.  I'd look for the stash though.