The early Enforcers with the oval milled area do appear to include a number of re-marked Envoys. If anyone ever got around to compiling a list of Envoy numbers, they'd probably find that there were a hundred or so numbers "missing".
Incidentally, Envoys are probably an even rarer rifle than an Enforcer. Not sure what the highest Envoy number is, but I haven't come across one over about 450.