You guys are so funny. LOL.
Already clarifying the rules and plotting it's use on Abe!
Ah, tis the season!
The letter written by the Magus as an AC , must surely have cropped up in the history of the OoH before 1220.
An easy Magic Theory roll would remind you of the actual AC.
In standard Redcap delivery , mail probably takes long enough to deliver that the AC fades.
It would not be hard to degauss all personal correspondence though.