Scrive Mark Zimmer: “This sketch, found on sketchleaf SV 329, page 3, is labeled “Rondo zum Concert in es mit Triolen”, or Rondo for Concerto in E-flat with Triplets. Probably Beethoven was envisaging some kind of virtuoso passage using triplets. The paper type has been identified by Douglas Johnson as belonging to about 1800-1802. This is far too early for the Emperor Concerto in E-flat, and much too late for the WoO 4 Concerto in E-flat (1784), so this is most likely is for some concerto that never was written. Joseph Schmidt-Goerg suggested that it might be sketch material for WoO 4, but this can only be seen as an example of a librarian valiantly attempting to bring order to the chaos of Beethoven’s sketches, his supposition not being supported by any textual evidence.
The sketch is not orchestrated, beyond a notation for oboe at the beginning and a “tutti” marking at the fifth bar. Beethoven writes “usw.” (etc.) at the end of the sketch, indicating that more of the same was intended. The last note of the bass line is supplied by the editors. Interestingly, despite the stated key of E-flat, the movement begins nebulously in a key of C major before settling into the tonic. This procedure anticipates the 4th Piano Concerto, op. 58, where the strings enter in the remote key of B major (bar 6, first movement), reaching the tonic G in bar 14, and also the Rondo theme of the same concerto, which starts out in C major, confirming G as tonic only in its 10th bar.”