Trex I wish I understood any of this.
It's all about the way that the law is interpreted - and the law (EN 15194) isn't very clear. The standard mentions a motor rated at 250w. It doesn't say maximum power produced.
Also many people get confused about torque and power. You need torque to climb hills and accelerate, not power, so you can have a high torque low power motor. The torque makes a motor feel powerful, but power is about speed (i.e. the rate of applying the torque). A standard 250w Bafang can provide enough power to maintain about 20mph on the flat with a 75kg rider as long as there's no wind. A Bafang CST, might have a lot more torque at 10mph, but if it can't go over 20mph, it doesn't have any more power. With motors cutting off at 15mph, they're deprived of the chance to make their maximum power, but they can still give high torque for hill climbing.
Using a watt-meter to measure power consumed is not much use either because efficiency can vary a lot depending on how high the motor is loaded.
If you take a motor like the code 10 500w BPM or CST with a 36v battery and 20amp controller, it'll peak at about 500w output power at 20 mph if allowed. At its maximum no-load speed of 25 mph it makes no power, neither does it make any power at 0 mph, so if you average its power over the entire speed range, it would be about 250w, so would you call it a 500w motor or 250w motor?
