Re: Can someone please explain the 23rd-and-24th-century starship clas
The one thing that the U.S.S. Hermes (one of the starships in Picard's tachyon detection grid) has going for it is that according to a canonical starship list Okudagram, that vessel is listed as "Antares class" (which was then reproduced in the Encyclopedia...more on that later). That means that Starfleet definitely has a vessel class called "Antares." Despite the Xhosa's plaque, I'm far more inclined to believe that almost all Starfleet vessels from any era share common characteristics, i.e. a saucer section and/or nacelles (but not always an engineering/secondary hull, but that's not important right now). I have no issues with believing that Starfleet, the Federation, and alien governments can have ship classes with the same name but are not in fact the same ships. The problem, as several people have pointed out, is that the Xhosa/Norkova does not share those characteristics at all. Perhaps if the modelmakers had built a more Starfleet-looking freighter for the Norkova (and eventually the Xhosa), there'd be no argument, but they didn't. They reused the Batris in a different configuration and at the same time used bridge interiors that were definitely Federation if not Starfleet.
The problem lies with the Encyclopedia and its outdated information. Okuda, Drexler et. al all but stated in the book's shiplist that the Antares from "Charlie X" and the Hermes from "Redemption" were the same class. However, not only did TOS-R reveal that Captain Ramart's ship was not a Starfleet vessel (and had no U.S.S. prefix), it was also not a class ship at all, if one believes that registries are chronological (the Yorkshire had a lower registry than the Antares and was the same type of ship). The Encyclopedia also did not provide class information for the Norkova or the Xhosa, which might be evidence that the plaque was nothing more than an in-joke and shouldn't have been taken seriously to begin with.
So what does the Hermes, which is undisputably of the Starfleet Antares class, actually look like? We could easily state that the design is conjectural a la the Rigel and Andromeda classes. Or we could say that the kitbash (whether filmed or not) is a viable candidate for the design, even if there's relatively minimal changes from a Miranda class ship. The registry numbers are, while presumably coincidental, quite close together. Conversely, this was just a kitbashed background ship that just coincidentally shares a name with a class ship only because of a rearranging of letters from two Reliant model kits.
I suppose at this point it's really rather up to any one individual's interpretation.