Alphabet unifications are meaningless (apart from almost certainly recognising a top world ranked fighter) once you can claim to be the lineal/undisputed/man who beat the man champion.

Pryor was the first ever IBF champ after being stripped by the WBA. The WBO didn't even exist in his time. I'm not sure whether Pryor was considered THE man from 1980 or 1983-1986 but he was certainly considered the top guy through this period.

Kostya wasn't THE man until the Zab win. This fight created a new linage.