I did a little rereading of the Vass book and some of the posts of DWFII and I think I have this right.
To clarify further: The 'Seam' or 'Inseam' is the row of stiches which attaches the upper to the insole. This stitch also typically goes through the welt strip in handsewn, welted shoes.
The welt stitch is the stitch which then connects the welt strip to the sole.
In my mind these are the two stitches, which hold the entire shoe together, that must be done by hand before a shoe can be called 'handmade'.
And no Goodyear welted shoe can be called handmade because the welt strip is sewn to the sole by a machine. (Unless the term 'Goodyear welted' is being misused.)
Someone will surely correct me if my description is mistaken.
Actually the term "Goodyear" means...technically and contemporaneously...that the welt and upper are sewn, by machine to a canvas rib that is glued to the insole. Fundamentally, the holding principle, holding the shoe together, is glue. And in a very real sense, nothing is holding the upper to the insole--there is no direct attachment.
Some people use the term "Goodyear" to refer to any welted construction...but that's not correct.