Without putting in exact XML structures, here is the summary of what is going on StarSystemDefs.xml.
Yellow Star Systems (System00), "HabitableZone" was changed from 4 max planets to 3 max planets.
Purple Star Systems (System08), "OuterZone" was changed from 3 max planets to 2 max planets, Asteroids look to have been added.
White Star Systems (System01), "NoRandom" (???) had 0-2 planets added; "Habitable Zone" was changed from 4 max planets to 1, asteroids look to have been added.
Blue Star Systems (System02), "HabitableZone" was changed from 4 max planets to 2 max planets; "OuterZone" had 0-1 added, asteroids looks to have been added.
Red Giant Star Sytems (System04), "Habitable Zone" was changed from 3 max planets to 2 max planets
Yellow Star Systems (System05), Changed from "Orange Star", "NoRandom" (???) had 0-1 planets added, "HabitableZone" was changed from 1 max planet to 3 max planets (this one DID increase)
Orange Star Systems (System06), "HabitableZone" was changed from 3 max planets to 2 max planets.
White Star Systems (System07), "NoRandom" has 0-1 planets added, "HabitableZone" changed from 2 max planets to 1, two sets of asteroids look to have been added.
Blue Star Systems (System09), "HabitableZone" was changed from 4 max planets to 2, asteroids look to have been added to "OuterZone"
Red Giant Star Systems (System10), "HabitableZone" was changed from 3 max planets to 2
Yellow Star Systems (System11) Changed from "Orange Star", "NoRandom" (???) had 0-1 planets added, "HabitableZone" changed from 1 max planets to 3 (this one DID increase)
Orange Star Systems (System12) "HabitableZone" was changed from 3 max planets to 2.
Exact XML data stucture can be found in the files in my previous post
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So, yes, this aside from the <Base>
IS the main culprit. Many many star systems had their max habitable planets decresed. By, like, a lot. So if we want to mod things up, here is one area we'd better look at. Simply because putting in too many star systems might make the game unstable.