I have a modest early to mid 20 Century helmet collection....
I had acquired an French "Adrian" to go with my Berthier
Was given an M17 “Brodie Helmet" in quite good condition
Next I purchased an M16 "Stahlhelm Helmet".
I had four major belligerents at that point.... ( the Brodie being the same pattern for both the Tommy's & AEF )
I figured to stop there...but
After some further study I discovered my French “Adrian" Helmet was in fact an M26.....Which led beyond the Great War
then my FFL gave me an M38 Luftschutz Helmet, this one needed some TLC , as someone had rattle can painted it black.
About a 1/2 pint of mineral spirits removed all of that revealing the original Luftwaffe blue...
yesterday I scored an M39 Soviet Helmet.
So I've advanced to WWII it seems