Go 10 months without molting - possible. Since they have been down for a while, they could indeed be molting. Once they dig down, they look for a place that is 'safe' for them - out of the way of traffic.
My small guy was down for about 4 weeks (if I remember correctly). He was in a corner giving me a window to his progress. I put a piece of black construction paper over the 'window' so he could have the darkness. Then one day I checked on his progress and he wasn't there. Just some pieces of his exo. He was walking around the tank checking to see if anything changed since his dig.
