Have you ever wondered if it's possible to measure the Kv of an electric motor yourself? The answer is "yes", and it is actually quite easy to do at home with relatively inexpensive equipment that you may already have. All that is required is a way to measure volts accurately (multimeter), a tacho to measure RPM and a drill press or another method to spin the motor at a constant speed.
Once you know how to measure Kv, you'd want to do it whenever you buy or rewind a motor, to confirm the Kv value.
On commercial motors, the stated Kv is usually a nominal value, because no two electric motors are completely identical.
Therefore, a manufacturer may round the Kv value to the nearest 50 or 100 according to what they measured on a test sample. In some extreme cases, manufacturers even publish inflated Kv values, hoping to take advantage of the notion that bigger is better. Some manufacturers don't even bother to give the basic specs, presumably because they don't know how to determine the motor constants.
And sometimes manufacturers make mistakes. E.g. when O.S. (who is well known and trusted for their IC engines), brought out their first electric outrunners, the specs for the OMA-3825-750 motor were horribly incorrect.