Add a postfix to the RecalculateCaches method (base game), CCL calls it every time a new car is loaded, and update your cache of liveries in it. That way all CCL liveries will be included.
This might also allow RSO to not need to reference TrainCarType_to_v2. This is desirable as that dictionary relies on all vanilla rail vehicles—including newly added ones—being defined in the old TrainCarType enum, which is not guaranteed to remain true forever.
From Wiz via discord:
This might also allow RSO to not need to reference
TrainCarType_to_v2. This is desirable as that dictionary relies on all vanilla rail vehicles—including newly added ones—being defined in the oldTrainCarTypeenum, which is not guaranteed to remain true forever.