I am putting this dress & jacket pattern out in multiple sizes a few months from now.
I began planning the pattern work up last year as I needed to complete the missing jacket back piece to make it available. Luckily, I had a little something similar (and in the same size) from which to base the missing piece (also a Simplicity), shown below. Doesn't always happen this way, but definitely make the process smoother.
The key here was to use enough of the jacket back piece from this design to make up what is just a side back of the jacket in the ensemble I want to complete. This required some rudimentary percentage calculation for scaling (shown below) the first attempt so I could then generate a CAD pattern of the piece and create a muslin test against the rest of the jacket pieces. I scaled the missing jacket back piece 'L' from the jacket back piece 'K' and drafted the re-created piece from the Simplicty 1432 back piece 'N' based on my calculations.
Here is the schematic showing what I wish to create and a schematic of the piece I used to arrive at creating it:
I'll leave off here for now and come back with the first iteration of the muslin trial.
Have a wonderful week!