Yes I agree Tod to make a mold like that would require more skill and a knowledge of set-up. I am sure this is the reason these molds had pieces and were not just one piece of wood.
I will try my hand at one of these a little down the road. Starting with a piece of wood I would cut my channel with the router and than using a jig remove the wood around it, again using
the router but with a different bit. After shaping the piece with the router I would remove the scrape using a table saw.
To make the jig I would use a layout tool to scribe my shape and than cut it out. You can get an idea of what I'm saying from the photo below..
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The blue area is my jig...