The Relaunch Litverse continued a bit after the new shows started to wrap up the political storyline and some of the other sequences. A trilogy called Coda concluded that timeline. Most fans have mixed feelings about it.
Una McCormack has one more book ‘The Missing’ which is the Pulaski one I mentioned.
The IP holder is the owner of the intellectual property and franchise rights. This shifted over time with the Viacom breakup then more recent. For a while Paramount had the movie rights and CBS the television rights. Simon & Schuster basically licenses from them to contract tie-in writers for hire. The IP rights from all the books stay with the IP holder. What the writers can do is limited by what the IP holder will allow the licensee.