The every so stylish Dolly Gray catalog from a 1929 McCall's Magazine brings us a choice of smart dresses semi-made. All the "difficult sewing and tailoring done, such as neckline, collar, pockets, tucks, pleating and all the novel French touches, beautifully finished for you in advance".
All you did was sew up the seams. This gave you "the priceless extra advantage of assuring a perfect fit".
I wonder why this method fell out of favor?