Most bullet makers over state BCs because they calculate them and of course use the highest BC
(Which was at the perfect conditions and not normal for most applications and altitudes).
The best way to find the BCs of a bullet is to shoot it in your rifle under normal conditions that you would encounter and with a good velocity you can plot the trajectory and end up with the actual BC
of a bullet.
Don't get caught up in the numbers game with bullets because it could be different from rifle to rifle
using the same bullet.
It can be misleading if used improperly. I live on the gulf coast where the altitude is 18 ft and the humidity is 98 to 100% most of the time and the numbers don't mean very much. so I test all of the bullets for accurate BCs based on drop charts.