I bought Galactic Civilizations III Ultimate Edition but 3 DLCs are missing. How come?

Indeed, there are only 13 keys in this bundle but they activate all 16 apps which are included in the Ultimate Edition.

If you redeem the key for the base game it will also give you access to the rest of the DLCs including the Mega Events DLC, the Crusade Expansion Pack and the Retribution Expansion.