If I had to dispose of surplus aircraft to prevent their use by an enemy I think I would drive the bulldozer over the crates a few times before burying them.
40 large crates at 4' below the surface requires a LOT of excavation - where would they get the time and plant to do that?
Any such work would leave a lot of traces, and it is unlikely that it could be hidden from the locals, who could be 'persuaded' to tell what went on.
Really hope I am wrong, but I doubt if anything flyable could be recovered.