It could be of interest if you'll show the cockade.Hi Giorgio, Great Question ! Its all to do with the cockade with this one.
Officers helmets were not stamped as they had to be bought privately and were not issued by the Regiment.
As you probably already know some states had different helmet plates ie Baden, Bavaria etc to distinguish them apart but some smaller states and in particular the Hanseatic ports adopted the Prussian Eagle plate. So they used cockades to distinguish them apart and show their heritage and traditions. I'll post some more pictures and do a show and tell of the IR76 cockade in another post.
Hope this helps.