Ian Brackley wrote:E. Castle, after examining extensive collections of antique weapons theorized that one reason the circular parry was not seen in French smallsword texts until the second half of the 18th century was due the weapons of the period c. 1680-1720 being heavier than examples one might encounter c. 1750-1820.
Although William Hope, in his early days when he still used the sword the right way up, was a big fan of circular parries, and whilst he isn't french the rest of Vade Mecum (1691?) seems pretty similar to contemporaneous french stuff. And come to that whilst Liancour (very french, same dateline) does not recommend the circular parry (contre-dégageant) he does describe it, and also teaches a big circular parry covering all the lines of attack.
I suspect that there are just aren't so many early smallsword texts so it's possible to overinterpret the absence of a particular technique.