You are absolutely correct.
So my thesis was: You are half or mostly correct but Aztlan stays the same, but apparently I just forgot or never even noticed...
->
My first reaction was: I have never seen Atzlan with planets after the gas giant with the 2 moons, so I tested it and boy was I wrong: Clean install in a new folder, vanilla game, so zero mods and standard settings (mixed, normal size). I generated 3 sectors, planned to do 10 but wasn't needed:
First one had Aztlan without additional planets, second and third try had different kinds of additional planets, many or all seemed to have Aztec or similar themed names.
In one try Magec also had an additional outermost planet orbiting the blue giant, just a space rock without atmosphere.
Note, and that I knew: Even planets which always spawn in the core may have at least different resource values, but while I do not know if the next one is true: I think at least the by factions inhabited core planets always have the same resource values, probably to keep the production values for the economy the same. <- probably more related to later player colonies and to keep some baseline things, like core always produces a min of X if not disrupted
I think Zorrah had in every try a different resource value. ^^
Boooyyy, I &%$!ing love the game for this. ^^ Some of the planets looked real &%$§ing juicy, can't wait to play the next patch. my_body_is_ready.png