If you are a Super User, you will still have the [MPGH] prefix alongside with your username.
Therefore, him having the Super User usergroup did not remove the prefix.
At one point when Ravallo was still a Super User, the prefix was still there.
However, as previously stated by Hunter; due to complete inactivity, the usergroup was removed, and later on switched to Former Staff.
The reason why he does not have the current [MPGH] prefix may be because his main usergroup is not set as "Former Staff".