As far as I’m aware, for most of NFL history, the league placed little stock in forced fumbles, and instead valued fumbles recovered. To my knowledge, there are no official statistics recorded for forced fumbles for the vast majority of NFL history, and Pro Football Focus only goes back to the late eighties.
With all that said, however, so far as I can tell—and somebody please correct me if I’m wrong—with his eighth forced fumble of the season yesterday, T.J. Watt set a franchise record for the most fumbles forced in a single season.