Thanks for that very detailed explanation. Now allow me to throw something else into the mix. I've been attempting to carefully reread the Notes & Letters of Theodore Gordon for about a month and taking my own notes of his Notes. I'm pretty sure that in one correspondence, I think with Skues, he describes how he differentiated the difference, but then throughout his Ns & Ls, he seems to use those words interchangeably. I haven't been able to find the specific Note or Letter though.
However, I seem to think that Gordon wrote that, through his readings of Kelson, Francis, Halford, Skues and other almost entirely British fly tying/fishing authors, 'fly dressing' meant 'to create a fly by hand and without the use of a vise' (okay Alan, a vice)? Maybe he was thinking along the line of a particular type of fly specifically a full dressed Atlantic Salmon fly (that's not a quote, just my italics).
I guess now I'm going to have to reread a lot of the book and find the passage in which Gordon talks about this.