I used to use ITN but now use
www.flyaow.com

I think this thing is not accurate now after years of trusting it.
Example plug in:

NRT to MSP on (NW flight 20) for January 25.
It is WIDE open with even 9 seats in K

BUT put

ICN to MSP on same date that connects in NRT to NW 20 for January 25
and it is showing full in back on NW 20 with only Y9 available

Try

SIN to MSP on same January 25 and is back to being wide open with K seats.

How can this be that they are showing empty but then if you want to commence in Seoul somehow the coach class fills up. Yes I can understand if there are no Y seats to seoul from Seoul to NRT bu that should not show up as affecting the CONNECTING (NW 20) flights load.

I am a decade old PLAT on Nw and I can never understand this thing..

Anyone with knowledge is appreciated!