There are a lot of variables that could come into play here, but most importantly the choke is not determined by the inside diameter at the muzzle, but rather by the amount of constriction from the bore diameter to the tightest part of the choke. Your measurements seem odd on the reproduction for the chokes listed. On the GH and Trojan, the actual bore diameters could be quite different between the two guns depending on the time period they were made. And of course chokes on older guns quite often have been opened up.
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