The latest contemporary pic I've seen (for W. Europe) of a spangenhelm is one which appeared on this forum not that long ago, of King Stephen, late C12. The development of these face plates seems to take in verey type of helmet in use at the time (ALSO the end of the C12), with a face plate bunged on the front.
Though I haven't seen specifically a spangenhelm-face plate combination, spangenhelms were just going out as face plates were coming in (though I slag Osprey off a lot, they have a book showing quite a selection of these helmets from Primary Sources, whih is worth chasing up - don't know its name).
As a logical progression, I would say you have a c hance that SOME helmets of this type may have just scraped in.
I take it this is an SCA helm, and there wkill be mail over the backplate, pretending to be a coif? Otherwise there is a problem - these back-plates don't seem to have come in till later.
Good luck with it
------------------
Egfroth
"I can hear the word
money from a distance of fifty miles, if the wind's in the right direction"
Major Dennis Bloodnok, Queen's Forty-Third Deserters (retd.)
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www.geocities.com/egfrothos