Yes I'm aware that is the official government policy, at least up until now: when you die, your SS# does not get reissued to anyone else. Or at least that's the way it's supposed to be. Of course Big Brother is far from perfect in clerical tasks such as this.
Maybe he applied for it while at Columbia...
The year the SS# was issued is inconsistent with with his time at Columbia: it was issued in 1976 or 1977, while he was at Columbia from 1981 to 1983.