Given where this map was discovered, it seems likely that these notes are from Arneson himself.
|Pre-production cover for Dungeons of Castle Blackmoor (2006)|
It would also be interesting to compare this map in greater detail to the floor plans of Castle Branzol which formed the inspiration for the original castle. In 2006 ZGG published Dungeons of Castle Blackmoor, but the book contained little information on the Castle itself. It has been speculated that both the Castle and the Dungeon could have been part of the never published DA5, of which there still may be a yet unrevealed manuscript out there.
In any case, this new map adds another piece to the puzzle that is Castle Blackmoor!