An esoteric post of interest only to French horn fanatics

Some time ago, a bunch of us hired a local conductor (at the time she was the assistant conductor of the Vancouver Symphony) to take us through Beethoven's 9th Symphony. (This wouldn't have been my choice, but I had no influence and was glad to have the chance to play anything of that caliber. We read it without any vocalists!) I would have jumped much harder at an opportunity to read the 7th symphony.
There was some competition between the horn players as to who would play the challenging 4th horn part in the third movement. I would like to have tried it to debunk a comment I read in the Pelican volume "The Symphony 1. Haydn to Dvorak" (1966). On page 167, Basil Lam (the author of the article on Beethoven) writes "That the occasional can influence the creation of the permanent is shown by the circumstances in which Beethoven wrote the horn solo in this episode.... The simple explanation is that one player of the instrument in Vienna had a primitive example of the valve-horn: hence the allocation of this elaborate solo to the fourth horn."
Well, I am a very half-baked amateur horn-player. Yet, though I don't own a natural horn (of course!), I have reproduced the effect by using the Bb side of a double horn, fingering the note Eb concert, and playing the entire passage using hand-stopping. It's a bit tricky, but very do-able. I don't know where Basil Lam got his idea: I have read that the valve mechanism was invented by Stolzel in 1831 or so and was first used in Halevy's opera "La Juive" (which apparently has 2 valve cornet parts) in 1835. Although Berlioz uses 2 valve cornets (in "Harold in Italy" written in 1834), where they are in A and Bb. However, he uses natural trumpets alongside the cornets, and always uses four natural horns. He does the same in Symphonie Fantastique. Even later, in the Brahms Trio for horn, violin, and piano, the horn part specifically calls for "Waldhorn" yet has many hand-stopped notes, though the valve horn was readily available by Brahms' time