Question: When have the bills been in the super bowl?
Disambiguated questions and answers: question: What years have the bills been in the super bowl?
Which super bowls have the Bills been in?
answer: 1991, 1992, 1993, and 1994,
XXV, XXVI, XXVII, and XXVIII
Natural Questions answer: 1993
1992
1991
1990 (from the Wikipedia article "List of Super Bowl champions")