The lapels will be finished with a heavy silk and cotton corded fabric, but before the fronts are covered, Susy sewed a layer of washed and preshrunk flannelette that covered the padstitching. This flannelette is trimmed up to the inside edges of the tape and provides a layer of cushioning between the thickness of the seam allowances that will remain in the front edge and the rest of the lapel. In other words you won't have a thick edge and then a thinner area- the lapel will have equal thickness from the edge inward. This will help when the lapels get pressed, now and in the future.
You would also cover the padstitching with flannelette for a satin lapel. In that case the flannelette also keeps the padstitching from marking the satin when pressed. You have to sew the flannelette in very carefully because you don't want any of its stitching showing through.
The third photo is of the step vent in the centre back of the coat. We usually finish this area before the whole coat goes together- it is easier to handle before it is joined to the fronts. The lining is also easier to arrange and slip down while the coat is apart. I only mention it because some people like to make up two complete halves or a tail coat and join them in the centre back last.
The curved back or "frock seams" are sewn to within an inch or so from the waistline. Once the side seam is sewn, the skirt will go on and then the frock seam will be continued to the waist and then down the skirt to the hem.