In the first entry, I asked whether a dart was an ornamental or a functional seam. The answer is functional. I think JC’s point of verb vs noun is telling. A functional seam is doing something, in this case it provides shaping. Shaping a garment is functional, it’s doing something, a verb. An ornamental seam is just something to look at, a noun. I am aware that many of the books describe this as an Osf-1 (below).
I think it’s a case of misinterpretation by one author, with subsequent authors copying predecessors. The description of the seam from the standard reference (751-a) is describing a pin tuck or a small sewn down pleat:
This type of stitching shall be produced by folding and stitching plies of the material near the fold with one or more rows of stitches.
Besides, until very recently, it was only narrow darts that weren’t trimmed. Again, I realize sewing books all say that we sew the dart and then we trim it away but this is generally false. When the pattern is made, we trim the dart away. The cut edge of the seam allowance more accurately shapes the dart because if the dart is not pre-cut, the shape of the dart is often anyone’s guess.