Here's a video of a Japanese luthier steaming the neck off a red label Yamaha FG-150. You can clearly see the shallow dovetail. Also notice, after the necks been removed, that when drilling the hole at the 15th fret, to get to the dovetail, he hit the part of the body. Maybe the 15th fret doesn't quite line up directly to the gap and people are missing it. There is an alternative view of the removal also. There is also a video of him showing the neck angle and straightness of the neck that also shows the approximation of where he drilled at the 15th fret. Also a video of him cleaning the the dovetail with steam. There also other videos on this guitar on his channel.
Videos don't seem to be working on here at the moment, so here are the links.
Neck remove for neck reset on YAMAHA FG-150
https://www.youtube.com/watch?v=T0hlj5J_GX0
Neck remove for neck reset on YAMAHA FG-150 - alternative view
https://www.youtube.com/watch?v=hkpR5ZtqB1s
Checking neck angle and straightness for neck reset on YAMAHA FG-150
https://www.youtube.com/watch?v=1EjaU9bnmvE
Cleaning neck joint glue for neck reset on YAMAHA FG-150
https://www.youtube.com/watch?v=WZAuyZXoTTw
https://www.youtube.com/results?sear...deyuki+higuchi