I believe those velocities over 40 yds are US figures. For many years in the US, shotgun velocity was stated this way. The Brits used the observed velocity over 20 yds from way back. This was at times converted to Muzzle Velocity. The early chronographs which marked a dropping rod simply required a longer time interval for accuracy so velocities near the muzzle were not reliable.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra