The P7 is NOT rated as being 900lm. The bin is 800 to 900 which means you wont get more than 900.
If you're lucky expect 850, assuming it is the bin quoted.

The problem with lupine lights reportedly is they don't us a MCPCB for LED mounting, just a normal circuit board... hence the LEDs run very hot.

I have no problem with people quoting bulb lumens as long as the design shows reasonable attention to optics/drivers/and cooling and they quote as bulb lumens not Out The Front (OTF). It makes the calculation easy, you measure your drive current and look up the lumen curve and the bin and chuck them all together. Not too long ago a certain commercial light maker was advertising 900lm from a triple cree XR-E light, he was multiplying the 350mA by 1/.35 to get the 1A lumens... didn't understand the efficiency goes down...

Take the magicshine which claims 900lm, but the driver runs at 2.4A and the LED is poorly mounted, hence the 400lm estimates its getting. Notice DX sells a lot of top bin LEDs...

Regarding dynamo lights and speed, not reaching max brightness until you're going at a good clip is a good thing. I don't want 680lm at 10kph.

Regarding false or misleading advertising, do you not have consumer protection laws where you live?