1. In case you are futher wondering, Lv11, two Vesper organizations (Medusa and The Inquisitorials) joined together to make The Vesper Interrogation Society, which is a mix between the two organizations. Medusa is no longer operational, as Vesper One told you. I now work as the leader of the Counter-Terrorsim Department.
2. Actually, you can keep your rank. Once, the Baroness was one of my top Medusa agents, and she still held your Vesper Six position, and Vesper Six has nothing to do with Vesper Three.
3. Vesper Three and Vesper Five are generally doing the same thing...however in the past V3&V5 had seperate departments. The department before Medusa was called Spying Club...stupid and useless and non-intimidating name.