Is it possible for two aircraft to have the same MSN number, I was under the assumption the an MSN was a unique identifier for an aircraft
Each manufacturer has its own conventions. For example, Airbus only use MSN (which is only unique per aircraft type). Boeing on the other hand uses both an MSN and "line number". Boeing's "line number" is unique per aircraft type (like Airbus's MSN) but the MSN is unique across all aircraft types.
Other manufacturers may or may not have the same conventions.