Oh, I see how that goes. The "slit" isn't a slit in the sleeve at all. The puff-part of the sleeve gathers into a "cuff" of sorts - that's the part that has the slit and curved edges, with the white piping around the edge. You'll cut that piece like you would a cuff band, only it's not sewn as one solid band. Follow the pattern for the puffed sleeve, until you get to the part where you would gather the sleeve and sleeve stay (the under-part) into either a cuff band or a lower sleeve or whatever the pattern has. You'll sew your "cuff" there instead. It's hard to describe with words, I'm sorry, I'm much better at pointing at pictures and gesturing.
Which pattern are you using for the puffed sleeves? I'm using a two-part sleeve for something right now and I could point to exactly which part would be done different.
As for the white knots and the small curve of piping that goes up on the puffy part of the sleeve, I would just make those separately out of cord or soutache instead of piping and sew them on top of the puffed sleeve so that it meets up with the slit in the cuff. It may mean hand-sewing on after you get the cuff sewn on, but before sewing the sleeve to the bodice.
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