Jeff, there are two further destinguishing factors between the early (1 and 2) and later (3 and 4). I believe the early executions had engraved casebacks, T on the dial and smaller sub registers. The later executions had plain/polished casebacks, no T and the slightly larger registers. There may be some overlap here but I have two early examples with these features as well as the later example.
More later when I get some time.
regards
Paul
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