Aaron,
If the Beethoven they dug out was burried 300 years ago, I am afraid they must have excavated the wrong grave. Perhaps one of his ancestors. The composer Ludwig died in 1827, only about 174 years ago. Maybe that is why the papers were blank? The older guy simply couldn't compose, only decompose.
Otherwise, concerning the main topic (lyrics or music first) I have tried it both ways around.
I used to write songs with a friend of mine who did the lyrics. He would take some song and write new lyrics for it. He then gave me these lyrics without telling me what he had used as a template. Imagine my surprise when we had finished a song, and he started singing the lyrics of "Mr. Tambourine Man" to my melody!
We also did it the other way around. Already having composed a melody, I would hand him a template something like 6-6-8-8 etc. giving the number of syllables in each line. My experience was that melody first produced the best results. We wrote a total of 23 songs back then, just for our own pleasure.
When writing on my own, fragments of melody come first, then some lyrics, then some melody etc. until first verse and chorus are ready.
Tom