The first problem by this article, is the origin of the corset.
The corset was a invention of Roxey Ann Caplin. And first common know in 1851. Most corsets before 1851 was a pair of stays, by motionless shoulders. It is important to understand that her petticoat Suspender the spreading skirts weight to the corset, before the skirts' weight was on the shoulders.
The girls used from about 1500 to 1950s a pair of stays. A pair of stays supported back then they better experience could carry heavy things on head and protected also back in field work.
Naturally then turn the ribs down, and a A pair of stays promises ribs horizontally. But by more options, some girl-corsets could turn the ribs upward. 
In 1908 all women of fashion have the ribs upward. But by buildup to the war, meant that many maids got work. This made it necessary to simpler dress, and there were several ex-maids had money and could buy fashionable clothes. But the fabric grow in price, by more buyers. The adult women would not go with the girl corsets, and could not get wasp waist.