Perf A was sometime ago, and did'nt really understand anyway, but I think the original poster was getting a bit confused as to what an overrun is.
At V1 and a failure occurs, Ac can either Go or stop, the stop part means that it can come to a halt within the Accel Stop Dist Avail,,,ASDA and from hazey recolection this can include grass at the end of the runway,or some other semi prepared surface, forget the exact definition, but it will not always stop on the Black Stuff.
So just because aircraft left the runway at the end can mean it was stopped within the prescribed ASDA.
Besides as J T said, perf figures are for a prescribed set of circumstances, as you have to base them on something. It's just that it is pretty unlikely you will have those circumstances afffecting you on the day you hear ""RING RING" " V1", and as John Coleman said " What happened next"" answers to..
Ring Ring is the firebell by the way..