And actually, some of my dead sims at least do seem to have "character data available".
ETA: And neither is unlinked.  Example:
hood;HoodName; NID;SimName;  FamilyInstance;SimFamilyName;HouseholdName;HouseNumber;HouseName;AvailableCharacterData;Unlinked
N004;Brenville;2;  Therapist;0;             (NPC);        Default;      0;          Unknown;  Y;                     N
N004;Brenville;70; Amin      0;             Bren;         Default;      0;          Unknown;  Y;                     N
ETA2: Interestingly, I have some other dead sims that have N for AvailableCharacterData and Y for Unlinked.  Note that Amin Bren's tombstone was lost and I haven't been able to recover it, so that might be why.  But there should still be some way of distinguishing him from the Therapist.