Between the 1979-80 and 1988-89 seasons, the Los Angeles Clippers had the highest point differential by a team with fewer than 13 wins and 10+ wins in a season, with a -937 point differential in 1986-87.
Interpreted as:
highest point differential in season 1979-80 to 1988-89 with less than 13 wins and 10 or more wins