When Harry was in the corridors trying to find Peter Pettigrew at night, Snape came. Snape took that map, and had a few attempts at revealing it. When he told the map to reveal itself in the name of Professor Snape, comments from the 4 creators appeared on the map. After each comment, they put their code names: Moony (Remus Lupin), Wormtail (Peter Pettigrew), Padfoot (Sirius Black), and Prongs (James Potter).
Would Snape not have recognized those code names?
One time, when Harry was taking Occlumency lessons with Snape, he had the chance to explore Snape's thoughts in the Pensieve. In the memory, the 4 friends always talked to each other using their code names. Snape could of easily heard what they were calling each other.
If Snape did recognise the code names on the map, why did he not react? Why did he ask Lupin what this "spare bit of parchment" was?