I like the idea, however I would actually prefer that they be assigned to "Departed Monk" (or "Apostate Monk" or even "Deceased Monk").

I'm not sure why I prefer Departed Monk over Anonymous Monk, repressed memories of bastardized databases floating to the surface perhaps. I think of Anonymous Monk has a specific definition of sorts and previously known monks don't really fit that definition, do they? So moving these monks to Anonymous Monk would tend to muddy the definition of Anonymous Monk. Having had to deal with some databases where folks muddied column definitions by reusing existing columns for new kinds of data rather than adding new columns as they should have (try extracting meaningful information from that kind of mess), I'm skiddish of changes that would tend to muddy the existing definition of something.