It can do more. It can also prevent the near-accidents that were only avoided due to the reactions of the other cars. Those are not in the accident tally, but are situations where the driver did something bad.
I had a driver pull out in front of me from a side street, I saw it coming and could brake in time to avoid T-boning them. If FSD had been on that car and not done that, it wouldn't get credit on any current metrics.
Regarding statistics, if an accident involves multiple cars, did that count as multiple incidents or one? If FSD gets in 2 two car accidents for every 5 car accident it prevents, is that improvement ?