Thanks for the comments, especially df's, which has filled some holes in my knowledge. It would be nice to turn up a Goerz serial number list, but at least for the Series III things are pinned down to a single decade.
So far as I know, the Hologon was also called 'Doppel Anastigmat'. Whether the use of the phrase was trying to trade on the good name of Zeiss, or whether it had just become a meaningless tag (like 'APO' today), probably went to the grave with the original designers.
My little Series III is a cute lens in a curious barrel. Tiny compared to the other 120-130 lenses I have lying about, but no iris and a mounting thread that places the Waterhouse slot behind the mounting board. I don't use it (I have modern offerings, and the oldie has sentimental value) but the big one will make a nice normal lens for my ULF.