One opinion is that the Vienna orchestra used 6-string bass viols, with the lowest note as F below the cello bottom C, not “modern” basses, and supports this with the fact that in some pieces Beethoven is careful not to write below F for the basses.
However first movement of Beethoven 7 has bottom C for the basses (and this also occurs in Beethoven 5) and that would be consistent with three-stringed Basses tuned in 5ths C G D, which were also in use at the time
The Viennese Violone was pretty well established by the 18th C. Mozart was not the only composer who wrote down to C1.
Knowing that Domenico Dragonetti played the premier of Beethoven’s 7th and that he tuned his 3 stringed bass C1 F2 C3 should help — if that’s the bass he played.
He also played the premiers of the 5th and 6th. Knowing that he tuned the bottom strings of his 5 stringed bass to C1 F1 Bb2 makes the 6th a lot easier to play — if you played a 5-string as I did. I’ve never seen that in a book but bassists trade such lore amongst ourselves. I learned that as a young man the first time I played it. The conductor, himself a bassist, made that remark casually at a rehearsal seeing I played a 5. After a couple days of practice, I had the end of the storm nailed down.
The 5th is easy on a 5 string tuned to B1 on the bottom as I normally did, C1 open or E1 with a C1 extension. It’s just not that hard. I know one player who keeps her standard 4th string tuned to C1 without an extension. The string makers have anything the modern player needs.
Where I live, the community and high school orchestras are the only ones anymore who do not insist on a bassist having the C1. Lots more slots then there are players to fill them in the amateur ranks. Even the part-time semi-pro orchestras require players to have that note. Collectively, they’re known as The Freeway Philharmonic to those players who have gigs in 6, 7 or more to make ends meet.