In terms of clear-cut mistakes, Klaestron
shouldn't be a UFP member. They were overtly hostile in "Dax" and made it clear that the UFP should keep out of their business.
I can't fathom how the idea first surfaced that these guys could be members - but it persists in so many books now that it may have to be rationalized somehow, such as with them all joining immediately after the events of "Dax" due to a revolution or something.
Also, you probably know my stance on Trill membership...
Yeah, it is kinda silly. Unfortunately, TOS did this a fair bit: Beta III, Omega IV, Omicron IV. And TMP gave us Delta IV. So, the original episode writer did probably intend for it to be a planet whose full name is Alpha III.
We could always argue that our heroes drop parts of star names when they are clear from the context. Either the place is so famous that nobody bothers to give the full name anyway, or our heroes are having their adventures that week within a specific constellation (a tight asterism) and thus drop the constellation name.
Alternately, we could argue that we are mistyping these names. It's not Delta IV, it's Daltay IV; it's not Alpha III, it's Alstha III; it's not Omega IV, it's Omygu IV. Odds are that most words in a foreign language will always resemble differently spelled words of different meaning in other languages - especially in the case of proper names.