What you say is spot on re the 'mass produced one offs'! As an aside, I have always been (dismayed?) intrigued by the use use of the 'humpback' shaped upper horn scratchplate used on the re-issues when my own and all the early Marvins as I remember had that part of the 3 piece scratchplate rather 'streamlined' - as this clip from 1965 shows.
