For my part, all else being equal, for every N criminal home invaders, the optimal number of home invaders repelled by lawful force without injury to innocent civilians is also exactly N. If you want to mix those relatively rare good mass shootings in with other bad mass shootings (the vast majority of them), that's one way to approach things. You could also keep a list of "Things that happened on Tuesdays in history" and it would be a perfectly self-consistent list.
> good mass shootings in with other bad mass shootings
I'd certainly say that's better methodology than trying to define "good" and "bad" mass shootings and then only list the "bad" ones. (I don't quite see what's good about this shooting anyway, but I suppose you mean that the crime was stopped.)
There is nothing wrong with the list, but there seems to be some metalinguistic dispute about what's the best definition of "mass shooting."
This dispute is merely about words.