More kirtle fun

I think I've got the pattern for my supporting kirtle sorted out (all by myself too! yay! And no free-range boobs!) I've decided to give the funky shoulder strap thing I posted about a couple of weeks ago a try, as this is an interesting problem and I really do like the look of the facing/strap/whatever around the neck opening.

I came across this picture which threw a bit of a wrench into things though:

The detail is taken from the Braque Family Triptych, another van der Weyden, dated about 1450.  If you look closely at the shoulder area, it looks like she's working the raglan sleeve seam again, but also a shoulder seam running down the top of the sleeve of the kirlte.  Which is weird.  This funny top seam doesn't extent into the shoulder strap section as far as I can tell, so it might just be some strange piecing in the sleeve?  But there's a bit of white shift poking out, so maybe the kirtle is sleeveless and the seam is the shoulder seam and the strap is just a facing?

As far as the shoulder strap idea goes, that's working out pretty well so far.  I'm actually getting something fairly close to the raglan type line at the underarm, where the armscye scoops up to the strap.  It's not as pronounced on my pattern but if I were to raise to neckline up a bit it would be (or at least it could be if I fiddle with things a bit, I'll take some pictures later once I have things as point where it's descent). 

I'm trying to decide what the best way to attach the facing at the top of the bodice to the strap and the main body of the bodice is - so far the bodice has a smooth line across the top until it dips down for the armscye.  I think the easiest way to attach the straps so it looks neat and like the pictures would be to make up the top facing bit with the straps attached to that and sew them on to the top of the bodice as a single piece to finish the neck, then attach the sleeve.  Or, put another way, treat the band at the top of the bodice as an actual facing and not as an extension of the bodice.  It might be easier to put the sleeve in first, then sew in the facing and the shoulder band.  Huh.  Now I've confused myself.