I've always wondered if Haydn and Beethoven knew the Prussians. They were, I believe, among Bach's better known works, but I could find no direct evidence.
No need to wonder: Haydn was a huge fan of CPE Bach, he had his book,
The True Art of Playing the Clavier and also many of his scores, which he says he "couldn't go to sleep last night until I had played them all through". The only candidates, due to publication dates in Vienna for various works, are the Prussian Sonatas. So I would say certainly he did.
Beethoven, before he moved from Bonn to Vienna, was a student of Christian Neefe, who taught him the keyboard by playing 'Old Bach's 48' (The Well-Tempered Clavier). It is unimaginable that Beethoven, like Mozart and Haydn before him, didn't also learn from
The True Art of Playing the Clavier. By the time competitive 'piano schools' came out, like Turk's, for example, Beethoven didn't need it anymore.

Don't know about the Prussian Sonatas there, although certainly the ones "
Für Kenner und Liebhaber"
