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.