I said the same thing, then went to fact check myself. Apparently post season losses are also vacated. Wikipedia:WikiProject College football/Vacated victories - Wikipedia
I'll leave it up to @GatorLurker, I feel like he should get to do the big reveal. Besides I think @legarto79 figured it out before me.
I HAVE SOLVED THE MYSTERY. In 2020, DIII Women's Basketball, Hope College went 27-0, advancing through the first two rounds in the NCAAT until the remainder of the tourney was canceled due to Covid. This is even better than Lurker's clue about a vacated loss. Nobody vacated nothin,' and it still meets the criteria of his original question.
I'm starting to think that the Wiki comment is a misinterpretation of the referenced material (which explicitly states: "The won-lost records for each of the opposing teams are not changed when games are vacated."). The reference to a loss not counting appears to only apply to the team having to vacate contests, and only in an NCAA Tournament (for the loss). I suppose all that really means is that it was not that they lost to a team that had to vacate their games, but they lost and were able to vacate that loss as the team that had to vacate tournament games. Go GATORS! ,WESGATORS
Another clue. The team that had to vacate had a player later determined to be ineligible. That player was named MOP for the tournament even though they lost in the championship game. And he never got the trophy.
HUGE clue. The team that was undefeated and the team that had to vacate are both in what was once called The Big Five that later added a sixth team. It is not a conference.
I don't think the NCAA agrees with you, Lurker. I know the team you are talking about and the year. The school itself doesn't even claim an undefeated season for that year. Go GATORS! ,WESGATORS
See my Maxwell reference above. They 100% lost a game, but we're not supposed to say who they lost to. Go GATORS! ,WESGATORS
In the 1970-71 season Penn was undefeated and eventually lost to Villanova in the Elite 8 IIRC. Penn had beaten Villanova earlier in the season as part of the Big 5 games at the Palestra. Villanova went on to lose to UCLA in the championship game. Howard Porter was the star player for Villanova and named MOP but he had signed with an agent in December 1970 so was ineligible.
I like GatorPlanet’s Div III WBB answer better. And that answer actually fits with the question as posed. Not to give Louisville, et al., any reinforcement, but yeah, what happened on the floor actually did happen, whatever later records say. And the team that GatorLurker was looking for was not winning the title without multiple upsets beyond what we’ve seen in the tourney.
Not only did Villanova crush that undefeated Penn team 90-47, to make matters worse for Penn they had to share the same plane home to Philadelphia with Villanova after the game. Coincidentally, that 1971 tourament almost provided two answers to the question as Marquette entered the tourney undefeated. Had they advanced one round further they would have played a Western Kentucky team that also had to later vacate all of their tournament victories.
Similar, in 2015 Thomas More apparently went undefeated and won the DIII women's tourney, but had to vacate the entire season afterwards. Thomas More vacates 2015 national title