A few questions from a beginner

[Nathan Ross]

owned by a lower ranked soldier?

The Theilenhofen 2 'cavalry' helmet (the big attic one), despite often being referred to as an 'officer's helmet', was apparently owned by an eques cohortis.

The Deurne helmet was marked STABLESIA VI - this could mean that the owner was a trooper (presumably - would officers need to mark their own equipment?) of the otherwise-unknown Equites VI Stablesiana, or an abbreviation of 'Stablesia Vicit' (the Berkasovo 2 helmet was marked 'Vicit Liciniana'), which might not be as revealing.