The same for me- I’ve only ever seen the top lever marked on the Ne Plus Ultra locks and not the case, covers or bolt. Going from memory I thought most were 6 lever plus the bottom ‘floating platform’ as Brian described it, so with 8 levers Ants lock does seem something a bit special.
looking at the components of the lock there wouldn’t really be an area well suited for stamping apart from say, the bottom cover that overlaps the bolt or the area on the main cover above the projecting nozzle. The bolt head couldn’t really be stamped as on many locks because of the central channel to interlock with the boltwork.
going from memory again, all the GP’s I saw with this lock always had the lock mounted in with the boltwork on the bolt case. They were a beautiful fit with 2-way boltwork, the lock protected from sideways force and also interlocking tight in the Tailbar.
kitbears explanation makes sense to me, perhaps Ants lock is from a rarer variation with door construction like a Milners, ie with the lock screwed to the door but with the boltwork still in the bolt case.
Never encountered one like that though, and from memory I only really saw the Ne Plus Ultras on the same burglary resistant models, but short of a really unusual application it does seem the most logical explanation?