Hey drstrip,
Interesting, but I've never had the problem that you describe. Even if there is a slight error that propagates down the board, it makes no practical difference as the same error propagates on the mating board so the fit is the same all the way down the joint.
I've never understood the need for all the fancy adjustable box jigs out there. To me, they just seem to be a tremendous waste of time required to adjust them.
I have three extremely simple box jigs made from scraps, one is for 1/4", one 3/8", and one for 1/2". Those are the only size box fingers I have ever needed to make. Each one is a piece of MDF with two notches and a tight fitting stick in one of them. Actually, one is two jigs in one, 1/4" on one end and 3/8" on the other (the stick is removable).
The bottom line is that there is more than one way to skin a cat, so do whatever works best for you.
Cheers,
Tom
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"There is no path to peace, peace is the path."
Mohandas K. Ghandi