For those so inclined there is an interesting article on the history of the channel bottom to be found at the following link.
Those here who were around during all of this may be able to confirm, deny or expand.
Anyone who’s worked around a wooden boatshed would have seen a channel bottom a long time before they were adapted to surfboards .
In the late '60’s I remember an article that was in Surfer Mag about the “channels” on the bottom of a whale and it questioned the possibility of adapting it to surfboards. They’ve been around a long time.