The study measures the totals before and after the ban. If the totals did not change, then one can reasonably conclude there was little to no effect (as that was the point of the ban; reduce bite attacks). The only way you could still justify the ban worked is if dog ownership increased after the ban, which seems unlikely (and iirc the study touches on that).

One would expect that this sort of statistic would be easy to find if it were true, given the advocacy of bully-breed groups.

I mean ultimately the burden of proof isn't on them. There are some statistics that seem to support them. If thess BSL bans worked, one would expect evidence to show that they did, but that's seemingly completely absent too. The vast majority of independent organisations seem to be against these bans.

If these bans worked, where are the statistics that show they do? What about the myriad of studies saying bite incidents are caused by neglect of the dog rather than breed?