601, with up to 2.5% of the full tank capacity as gauge error on most Boeing jets you must have been a mighty good soothsayer. Add to that even small differences in SG it is easy to see how people are not really aware of exactly how much juice they have.
I have flown all manner of commercial wide and narrow body jets and whilst I have had a reasonable idea of my fuel state, I wouldn't stake my life or career on categorically stating what the real fuel state is.