Ad hoc sports statistic time

At espn:

For exactly 28 years -- spanning Dec. 30, 1980 to Dec. 30, 2008 -- there was never a day on which two NBA teams with winning percentages of at least .800 through at least 30 games of the season both lost. It's happened twice in the past six days, as the Celtics and Cavaliers both lost Tuesday and again Sunday.

Thanks, sql! Although it makes one wonder: when was the last time there was a day on which two NBA teams with winning percentages of at least .800 through 30 games both lost--and whose team names both started with the same letter??!?!?