> institutional memory.

Yes, exactly. Thank you for this phrase. There's also a certain amount of institutional bonding (to coin another phrase) involved with these people, in that they're sort of "mother hens" who take care of everyone.

Definitely not cogs, but I'm not sure anyone is who actually belongs in a particular office. Cogs are (generally) apathetic, at least in their machine counterpart. In a team scenario, "apathetic" usually translates to some kind of burden being shifted to the group.