I think we'd all enjoy seeing some pictures if that's possible.
H20217-4 is the reference rather than the serial. The serial is the 1'8xx'xxx number.
I personally think this particular reference is really attractive and interesting. I'm not sure I would go as far to say that it was rare but there do seem to be less examples with these triangular hands than the other 20217-4 references. I think this is because these are quite late and the bumper 20217 references were soon to be replaced with the microtor references.
Your point about the dial being a genuine gilt dial rather than printed is interesting. I had always thought that all Polerouters had printed dials. Is that something you've studied with a loupe? It would be fantastic if you could capture that in a photograph.