Just a bunch of notes:
Advanced Knife Bro is Mhanlen on BLF.
Just an open tube like that can cause throwy lights to read a bit higher than floody lights. They don’t really seem to diffuse the beam.
If you want a reference light to calibrate your own lumen tube, Maukka is selling some. More details here.
Okay, back to your situation:
Even if your lumen tube and calibration were off, I would still think the GT would read higher output than the TN42. Is your TN42 also NW?
One thing I’ve noticed about the GT is that it’s huge reflector moves the led a lot further away from the lumen tube opening which reduces brightness in the tube.
Also, the large reflector tends to absorb more of the leds output than a smaller reflector.
Maybe if we could measure the raw leds or use the same reflector on both lights, we would see the GT have a bit higher lumen output.
The bottom line is it’s a difficult light to measure lumens on.
There shouldn’t be any doubt the GT throws further. The TN42 is in the 600kcd to 700kcd range and the GT should be in the 1mcd to 1.3mcd range. I would go ahead and measure that. If you see this same big gap then your GT is doing higher lumens than your lumen tube is reading.