media Something random I don’t understand

Why does everyone say Silence of the Lambs was the third movie (after It Happened One Night and One Flew Over the Cuckoo’s Nest) to win the five “major” Oscars (actor, actress, director, picture, and screenplay), when Kramer vs. Kramer did it too, in 1980?

I’ve been reading about Kramer vs. Kramer just now, and I cannot find a single explanation for this. It won the same five awards, but it seems to be a secret. Or else both Wikipedia and IMDb are wrong in their records.

I hate it when things don’t line up.