In the beginning I was lucky enough to work with experienced contractors who had grown up working for their fathers - so the knowledge we had access to was deep and broad. Later the crews pretty much knew each other and if there was a real problem we could ask everyone (and their fathers!) for their expertise.
In my experience neither they nor the men who did finish millwork had ever been taught about any kind of regulating lines being used to determine proportion or design. They certainly have been interested in the ideas.
Circle geometry is beginning to be taught at forums of the Timber Framers Guild.
I met architects 40 years ago who knew about the Golden Section. I know only one architect today who is familiar with the Golden Section as it applies to architecture, but have not been able to have in depth conversations about how he uses the proportions.
I would welcome information about who is using all the variations of regulating lines and where. Earlier posts outline what I know at the moment.