There are no scores/100. The numerical score doesn't really correspond to anything. The NBME creates an artificial mean of 70, therefore that should be the 50th percentile. They also create a standard deviation of 8 so a 78 would be one standard deviation above the mean. If it were a normal distribution, that would be the 84th percentile, but I dont think it is so it's basically impossible to know what percentile you are in.