If you have eggs in places other than the nest boxes, that does not mean that there is a shortage of laying boxes. My chickens have proven that 2 nest boxes are sufficient.
Yet I have found eggs in many places in the past. eg: Under the perches in a corner on the poop board. In the large flower pot they use as a sand bath, on an old side table that I once put in the run. In a bucket under the nest boxes just outside the run, etc.
And if a chicken gets broody, sometimes she searches a spot outside where it’s quiet , hidden or even crazy to start breeding (on the neighbours compost pile).