Can anyone do better than I managed to do, which is:
find a before-the-Internet biography/article on Beethoven
(there are tons of them)
which does NOT say:

"this author is unknown / Unbekannt."


It isn't difficult, with the World Wide Web and
digital files from library archives, to locate the poem
written and printed by Friedrich Haug;
a simple search on Beethoven's lyrics pulls up both that newspaper
and the volume of Haug's collected poems.

I have searched at some length, though, for a pre-computer-world
author/commentator who cites Haug, the poet, or
comments on the poem from which the musical setting takes the lyrics.

It would seem that, for a couple of centuries,
the source of the lyrics has been hiding in plain sight,
the poem gathering dust in the library stacks.

At least, everyone seems to agree that
Beethoven himself offered not the slightest clue
to the Author's identity or where the lyrics came from.