"Factorio and Conquer: Tiberian Dawn" is not a Planet Mod, its more a mod with a list of C&C features that automatically get added to every existing surface and as such it doesnt add its own Planet, not even a new Surface in general.

From what I could tell, it does actually add a new planet, separate from Nauvis, and under default settings, the Tiberium resource only spawns there, making it different from the other planets, so I think it counts? You might be thinking of an older version, perhaps, but with Space Age enabled, the Tiberian Dawn mod definitely adds a new planet.

i was looking at the current version of the code on the github that the mod links where i could not find any api call that would create a new surface or associate the surface with a planet.
if thats outdated then there "code source" is outdated which is the newest thing i can look at without specificially downloading the mod just to analyze it.

Never even thought to look at that lol. Seemed easier to just.. download it and try it myself.

But considering the latest release on the mod portal was two days ago, while the latest commit on the github was from two months ago, "source" is definitely outdated.

EDIT: Just looking at the info.json on the github, it's clearly still the 1.1 version of the mod

ok, then apparently i was looking at the old version of the mod that was before it made its own surface.
as a developer first and modder second my habbit is to go on github when i want to look at the "source", especially since some of the most popular modders in the community first updfate on there and then push the changes to the mod portal.