Kevin Sutton wrote:

>Pre-Haydn, composers did not use the triplet as a rhythmic figure in
>simple duple meter.

I'm not sure this is correct.  Bach's Chorale prelude In Dulci Jubilo
(Orgelbuechlein) is, I think, notated in 3/2, and uses triplet divisions
of the beat.  Unless you mean duple in the strict sense of 2 or 4 beats to
the bar.  But I took you to mean in duple subdivisions.  He actually writes
duple subdivisions against triple, and later writes two unequal notes to
synchronize with the triplets in another voice, suggesting that he was
aware of the distinction.

Chris Bonds