Progress is obvious, at this point, for which I'm grateful.
Have finished and attached the new collar panels to the rest of the collar. They look a little strange up close, but less so from a bit further away. Still berating self for making the original too small. Will get photos of that once I attach the collar to the body. Have also sewn the shoulder seams that weren't in the original, and inserted the neck gussets.
Have mostly been putting together the sleeves, though. As you can see, at right, I've taken
liadethornegge's suggestion for hemstitching, though with a variation. The very wrist end of the sleeves had a bit more fabric left over, so I've edged it a little differently to minimise the visual impact by drawing out threads at 3 and 7 threads away from the embroidery, but only hemstitched the outer (doing both looked kind of funny--ought to have drawn two neighbouring threads--learn and live). Like I mentioned earlier, each cuff was too long, but rather than unpick Holbein stitch or cut the embroidery, I've just folded the edges under to keep structural integrity. It's edged in buttonhole stitch.
I'd thought to gather with an obvious thread because the original Pemberton portrait has little speckles where I assume the cuff joins the sleeve. Gathered the ends of the sleeves by stitching to the count of 6 threads, then pulling the fabric to be the same length as the cuffs. Tied off, ironed--and whipstitched the cuff over the gathering thread because it didn't look that much like the original. I think the stitching is just decorative, now, rather than functioning for gathering. Oh, well. Also whipstitched the sleeve to the cuff on the inside, too, as this particular cuff doesn't fold over to hide the "wrong" side, like the cuffs do in the Warwick shirt. My embroidery is too reversible to hide the wrong side.
The underarm seam I'd intended to be interlaced insertion stitch, as I'd heard from the WMS, who have sent me a .pdf of their accession records that is quite descriptive of the shirt in question. Have made the stitches too close together for anything more than single-herringbone stitch to look good, though, which is somewhat awkward and cause for unpicking my attempt at double-herringbone without the interlace, but it's still pretty shiny.
Have sewn the ties on a little prematurely, just to give you an idea what the finished sleeve will look like. I'm rather happy with it, even if I've deviated from my plans by rather a lot at this point. May need to call it something other than Warwick, as I've really not used many of the Warwick techniques for it.