Thanks Joe for pointing me to this interesting article. This would seem to suggest that the Bavarian wappen is not an original attachment however, there also remains the possibility that this Bavarian helmet got reissued at some point to a non-Bavarian unit?
Is the latter at all possible?
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Appreciate this prompt and helpful response. "JR150" does indeed appear on the other side of the rear visor. Is there an authoritative online - or print - reference that would allow me to decode these myself?