Pretty good. While Roland was chasing the jumpers, they caused all sorts of damage, took some vehicles and jumped with them, popped in and out of public places ... If this battle between paladins and jumpers had been going on for centuries, as the movie said it was, it would seem that somebody would have noticed all the strange occurances. It's hard to imagine David not knowing there were other jumpers, or that it wasn't common knowledge. But hey, it's just a movie.