I've been making my pattern alterations this weekend and this post is specifically for the sleeves.
I measured my existing sleeve length on my first Jackie, which sits just below my elbow with the cuff turned back and I need to add 7" or approximately 18 cm of length the get the cuff resting just above my thumb joint. This will give me another nearly 2" of length when the cuff is left unturned, perfect for when it gets chilly.
The Jackie Sleeve pattern piece looks really long but a large part of the bottom sleeve is for "fold back" allowance. Because of the size of the actual sleeve I made up a little mock up for pictures as well as some drawings.
Here is the sleeve as is. The main fold lines are the ones on your pattern piece indicated with the arrows. You also have a couple of notches that are guides for your folding as well, which I have marked as a red line for clarity. The lines for the interfacing piece is shown in a light blue.
Use a ruler/straight edge to keep the grain line lined up and insert a filler piece of paper and measure gap to your appropriate amount. My extension is 7".
Fold the sleeve up along the line at the start/bottom of the two arrows. This is the fold back for the sleeve hem. Of course, when you are making the actual jacket, the sleeve hem gets folded under and the cuff gets folded "up" but when I took these photos I did them both "up".
Fold up again for the cuff. You are are lining up the bottom fold line to the top fold line marked on your pattern piece and shown by the arrows.
There is your nice cuff, and your pattern edges for this section should all line up nicely in a nice smooth line.
With a ruler/straight edge, draw in the line for the extension sleeve seam. To keep the line true you will find you will trim off a little off each side of the cuff fold back. How much you taper in your sleeve is up to you, I only did the bare minimum as I like the full raglan sleeves.
Fold you pattern pieces back down and you can see you have lengthened your sleeve and also trued up the cuff and sleeve hem turn backs.
Here is my actual pattern piece lengthened. It's looonnnng.
For the sleeve lining, I just extended it 7" and then laid it over the top of my lengthened sleeve pattern piece to make sure the width matched on both pieces. And it does.
Here is an infographic of the above if that helps. Just click to enlarge:
So that is my sleeve extended to full length. I will show how to extend the coat length in another post, as I think that is long enough for now. Any questions (or corrections), just leave a comment.