Hi Michael and a late thanks for your warm welcome!

First of all, I am sorry for any inconveniences caused by my edits. I've indeed been quite incautious in the selection of nodes during my orthographical delirium, won't happen again!

Regarding the remaining nodes: My decisive source concerning the spelling of Viennese suburbs and streets in general is the "Wiener Nomenklaturkommission", updated in 1999 after the enactment of the German language reform. (https://www.wien.gv.at/kultur/archiv/nomenklaturkommission.html)

In the section titled "Sonstige geografische Namen", Unter-St.-Veit is even listed as an example for this specific spelling rule, which led to my edit on the place=suburb node. As you've already realized, the spelling of both suburbs is and has been very ambiguous ever since. Local businesses and organizations rarely use the spelling with hyphens for the sake of design - which is totally valid and common elsewhere. According to Wiener Linien, even the underground stations are merely spelled this way on paper "as a provision made to safeguard existing standards", which sounds quite contrary to me. Upon further research I found out that the German language even invented a word for spaces mistakenly used for compound words: "Deppenleerzeichen" or - more sarcastically - "Deppen Leer Zeichen".

As for OSM conventions, I wouldn't know which one to adduce first. That "[you] should be aware that street signs may contain errors" sounds very logical in my view, but Ober- or Unter-St.-Veit is never referenced on any street sign (besides "Sankt-Veit-Gasse", which ironically uses hyphens to fulfill its role as composite noun). Additionally, street signs using an old spelling variant (like Nussgasse, formerly Nußgasse) don't have to be replaced immediately, only when affixing new ones. This led to my conclusion of prioritizing an official nomenclature. On an unrelated note which is not a concern of mine: Isn't the "don't use abbreviations" rule broken here? Shouldn't it be "Ober-Sankt-Veit"?

I'd love to hear your opinion on this stance, e. g. whether or not to index the "different kinds" of spellings in tags (alt_name?).

Kind regards,
Yktan