Yes, for the most part, it will be explained in RP but I can do so now too. Basically, Sanctum is split up into cells, some handle technology, some military, some diplomacy, some public relations, etc.Cells are sort of different task operations that work independently, so someone from one cell won't have access or knowledge to information from another cell. This makes it much harder for a mole to infiltrate Sanctum. Bella Nunez, as Commanding Officer has oversight to all of the cells, but each cell has Project Overseers. The team belongs to the Phoenix Cell- a cell that focuses on training protocol. Animal and Guardian are the Project Overseers for this cell.
Now that I've explained that, the labeling system works like this. P501 would be Ambrose's label. He is the first (01) of the fifth generation of operatives in the Phoenix Cell. I hope that makes sense.