From this weekend's USA TODAY:
Beethoven\'s lost oboe concerto performed

Interesting article. But, it appears that they still never had the entire piece as written by Beethoven.
 Quote:
Now, two Dutch Beethoven enthusiasts have pieced together the musical clues, put them into 18th-century orchestral context and reconstructed the second movement of the only oboe concerto Beethoven ever wrote...
And...
 Quote:
Scoring the orchestration, they inferred harmonies from the way similar concertos were composed at the time, Van der Zanden said.
I can't help but think: isn't that a little like someone writing down the melody with the guitar chords written above the clef (like pop music)? The only difference is they "inferred harmonies from the way similar concertos were composed at the time..."

Anyway, interesting piece of hisotry, none the less.