I see nothing produced by skeptics as to how the tricks were allegedly done, that is to produce items embeded in actual coal deposits artificially. Can you show how the tricksters allegedly did it?
I've seen, someplace that I forget, a discussion that hypothesized that the coal around the cup could be formerly loose coal accumulated around a cup dropped in a mine, cemented together by any of various mechanisms (e.g. limestane accumulation from percolating water). There are lots of ways in which such an artifact
could have come to exist. Only professional examination can colapse the many possibilities into a few possibilities or one possibility.