I bought a mystery hone on the Bay yesterday based solely off the wooden box. It may be a dud, but it was cheap enough I was willing to take a chance. The reason I purchased it was due to how the box end pieces are joined. They are not rabbet joints, but a rabbet dado which seems pretty unique in hone boxes. I may be wrong though and perhaps the rabbet dado was used all the time, but I guessed it was indicative of Thuringian/Escher type hones. The only real red flag about the hone I bought is the size is way too large for it not to be a one in a million chance. Here is a picture of the joint style I am talking about.
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PS This may be a giant mistake in giving up a secret to figuring out mystery hone origins, but what the hey....