Is it lined?
It's designed to be unlined and the ones I've made have been unlined, although I have made my own adapted facings to better support the back.
On the first version I used a HongKong binding finish and you can see the pics of that on the review on PR (together with the adapted facings). On the others I used overlocking to finish the seam allowances after stitching the seam.
Provided that the lower sleeve is widened a bit, it would be fairly straight forward to line it by using the same pattern pieces. That said, because of the (unstable) grain direction on the centre back seam of the yoke, I would stabilise the lining for that section by either applying a woven interfacing to take over the grain or adapt the pattern pieces to get the back yoke of the lining on a stable grain.
This is one of those designs where the choice of the colour/pattern of the fabric makes a great deal of difference to how it looks when worn.