Has he never heard of dewaxed shellac? And I'd bet I could duplicate the
color he's after by simply mixing a little brown mahogany dye with Zinsser
Sealcoat. I know I've matched alder with a weak mix of the same. I'd
also bet that the oil stains and varnish don't stick to waxy shellac
very well either.


It is not a matter of overall color; he is trying to control the color of
various parts of the grain and to add depth to the finish.
Personally I can't see it, but perhaps he can.

I read a book by a Nobel Prize Laureate who advised the reader not to feel
bad if he can't grasp quantum mechanics intuitively, as the author can't
either. In fact, he suspects that anyone who says they can is deluding
themselves.
It may (or may not be) the same with those who require 4 stains to achieve
the desire effect.