found his old book in the online lib.
alone for the type Weisenau, H. Russell Robinson had different classes
Imp Gallic goes from A-K with subclass naming from locations
Typ Nijmegen
Typ Worms
Typ Augsburg
Typ Aquincum
Imp Italian goes from A - H
Typ Cremona
Typ Mainz
Typ Hebron
Typ Niedermörmter
at least 4 classes are considered derivates of this helmet, Auxiliar helmets A - D
but after 1975 a lot of work of adding classes, locations, variations proven from sometime only two or even one archaeological found are given, differently named in different countries
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how fine this differences are, can be shown from the reenactment scene.
a simple start i.e.
http://www.imperiumancientarmory.com/Helmets_Gallic.html
better
http://www.imperiumancientarmory.com/Helmets.htm
EDIT:
http://www.armae.com/antiquite/11antiquitecadre.htm for sideviews mainly
here you find also a clue, that the
Unit_ROM_Mid_Empire_Legion4 (and others)
is close to the Aquincum helmet
which however is not a that large jump in the timeline, that you could say it was used mid. imperial time
...not paid by AGEOD.
however, prone to throw them into disarray.
PS:
‘Everything is very simple in War, but the simplest thing is difficult. These difficulties accumulate and produce a friction which no man can imagine exactly who has not seen War . . . in War, through the influence of an infinity of petty circumstances, which cannot properly be described on paper, things disappoint us, and we fall short of the mark.‘
Clausewitz