It’s worst with TV & Cinema, not knowing when to stop. I’ve two major series, one SF and one Fantasy. The temptation is like Pern or Chalet School and to keep extending. Except unlike the the Famous Five the characters age and change. Unlike the excellent Midkemia world, both have major social, political, economic and technological changes. The Celtic Otherworld of the Inamok development somewhat influenced by my own engineering background and interest in vintage electronics. I wrote a history of Communications and Computers with their convergence in the 1980s as a background for a project. I also spent many hours with Civilisation II and IV. Those games seem well researched.
I think “Carmán’s Legacy” (book #14 of Celtic Otherworld) and either the “Mission’s Talent” or the “College Talent” (#7 and maybe #8 of Talent’s Universe) will tie up all the loose ends. I’ve chopped up the “Second Talent” and put bits into “The Legal Talent” and “The Mission Talent” as it only reached Novella length and the plot was weak.