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Fred, 

These are certainly interesting discrepancies, and you may well be right. There is another possibility that (possibly) fits with another clue. The "nametag" on this sextant suggests that it was in some way custom-made, either for a merchant or maybe for an individual, possibly as a special gift (for example, upon entry to or graduation from a navigation school). If it was tailored for special requirements, some of those discrepancies could make sense. If you were ordering a presentation sextant, as a gift for a "favorite son" perhaps, then you might order aesthetic upgrades, like a wooden handle in place of bakelite. Just a thought...

Frank Reed