Davide, check the weights on the product page. They are based on averages from real production. And the difference is not just a fiber layer change, the whole layup is different, hence the 12-15% difference (on EVOs, haven't checked other boards).
I have to go and dig out one of the hollow boards. They had the vent screw in the nose so maybe you could have someone fill the nose up with half a pound of clay. Or not. Then go ride and try to guess which is it.