For example, I just found this:
Frank Herbert in Chapterhouse:Dune wrote:She fell into a semi-reverie, still alert to the sounds behind her, but relishing the evidence of new victories that had been displayed to her this morning. She liked to roll the names of captive planets silently on her tongue.
Wallach, Kronin, Reenol, Ecaz, Bela Tegeuse, Gammu, Gamont, Niushe...
Contributor of Ampoliros entry in the DE wrote:AMPOLIROS, LEGEND OF. A pre-Guild legend appearing on many planets, including Arrakis, Ix, Kronin, Reenol, Ecaz, Caladan, Bela Tegeuse, Giedi Prime, Gamont and all the planets of Niushe.
If I'm not mistaken, Kronin and Reenol aren't referenced in any other book in the Chronicles.