It's not that the light-manufacturer is lying, they are just using the LED-maker's maximum output at the LED under maximum drive. A Cree XML-T6 LED can put out 1200 lumens at 3.3amps usage. But no one is really building lights that draw that much current, too inefficient and too much heat generated, requiring a copper heatsink and beefy driver-circuits. Most light-makers will use 2amps max for about 700lumens at the LED. Then after going through the optics, you're really looking at about 500-550 lumens OTF - off the front.

I've upgraded many of these lights from the P7 flashlights to MS headlight copies with my own adjustable drivers so I can incrementally creep up to the LED's maximum potential. It's amazing the difference between the off-the-shelf 500-600lm output versus unlocking the LED's true 1200lm potential! Of course, now you're looking at only 40% of the original battery-charge life and I've blown quite a few LEDs by overheating. Many don't come with sufficient heatsinking to drive the LEDs at maximum; and copper works much better than aluminium.