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The earliest photo I can find of the table, a b+w of an unstained walnut example in "the Design of Herman Miller," seems to show both elements having the same slight concavity to the long horizontyal edge -- which would be typical practice for a "sled" base ? The photo clearly shows the bulge of the vertical curves to be as you describe. . .
I have assumed that the two wood pieces are intended to be identical, though I have no confirmation of that.
The design is a good one for a wooden item, as the glue-up includes several very short lengths, which are a natural by-product when cutting defects like knots from a wood like walnut ! I suppose an experienced manfacturer would quickly spot such a potential economy in a proposed product. . .!
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