My 2018 S with PT keeps about 10 miles in reserve after you hit "00". I guess the smaller the battery, the smaller the reserve. But in your case, it would appear to be a negative reserve.
My 14SR consistent died at 6% indicated SoC. Haven't ridden the 16SR down often enough to see a pattern, I haven't felt a need to push distance as much with the larger battery..
The one time I rode my 2014 S with PT down to empty, it stopped right as the range indicator read "0". Unfortunately, that was at the bottom of the hill that I had to climb to reach my home. I tried pushing the bike, but became exhausted after about 5 feet.
So then I turned off the ignition, let the battery pack rest for a couple of minutes and obtained enough power to slowly move about 100 feet before the bike stopped again. I did that about 5 times before making it to my garage. And that was the last time I ever tried to exhaust the battery pack on that Zero.