My impression was that they were deliberately taken in rather than swapped over. I guess if your boots were just about useless after being re-soled/nailed to the point of the uppers no longer holding then you might take the old pair in then. Each chamber and often junctions had a boot. The last bite of a crust orapple core was often into a corner on the way out...which I imagine must be the same kind of thing as the Cornish one. So many things we don't ask when young. The similarity of the names for these characters and the fact that the same symbology is commonplace around the world amazes me. In part I know it is due to the export of miners/engineers in the 17/1800's.