I believe that as long as a forced fumble occurs, it counts regardless of who recovers. As far as the fumble recovery for offense, that is another story, dealing with who recovers it, where and what happens for the rest of the play. The idea being it disrupts the play and should be recognized statistically. If it's not recovered by the defense, that doesn't take away from the play he made. I believe it's possible to look at defensive stats and see more fumbles forced than recovered because of this. I'd look it up, but I'm not sure it's even in the rules. Maybe looking to the NFL woud be better.