Hey Johanna,
Very perceptive questions!
1. I gave you a little extra width in the skirt back placket for “turn of cloth” and because the testers felt it was a bit tricky to sew. It felt safer to have a little extra there, but if you match the crease to the line of stay stitching you’ll be fine.
2. With regard to the difference in width on the skirt due to the placket, I agonized over that detail and in the end decided it was best to center the placket for the sake of simplicity and because the difference is negligible. Since the skirt edge is curved, the longer edge can easily be “eased in” to the bodice. The shorter side is exactly the same length as the bodice, so you may need to clip into the seam allowances of the skirt in order to match the seam lines, depending on your fabric. Most fabric is stretchy enough along the width, and the curved edge will stretch a bit to help you fit it without clipping. But if you need to clip a bit, don’t be afraid to do so. I hope that helps!