Ah, it's probably installed then. I think devs were going to use the DLC folder but didn't. Everyone has the DLC\Supernova\placeholder.txt. If you look in the Data\Gameplay folder you should see something like ShipComponents_Cent.xml. The first DLC is mostly an event pack. The second is going to rework combat quite a bit.
Here is the description.
"Dive into the 24th-century Centauron sector, a melting pot of galactic powers like the Drengin Empire and the Altarians. This DLC enriches Galactic Civilizations IV with unique technologies, planetary improvements, starship components, executive orders, and a new mission: Return of The Korath. Experience dozens of new lore-driven events that bring the galaxy's story to life. These features also extend to custom civilizations sharing traits with canon species, offering a more personalized and immersive gameplay. "Tales of Centauron" promises an expanded, dynamic universe, deepening your strategy and narrative experience in the Galactic Civilizations saga."
It can be difficult to know where the DLC begins and ends.