Slytherin wins both the Quidditch Cup and the House Cup (1990)

New Gryffindors are told about the House Cup by Nearly Headless Nick

“Gryffindor have never gone so long without winning. Slytherin have got the cup six years in a row!” (PS7)

Harry speculates after a hard Quidditch practice session

“If they won their next match, against Hufflepuff, they would overtake Slytherin in the House Championship for the first time in seven years. ” (PS13).