This concerto for 2 solo horns and orchestra raises a number of questions on the basis of its sources. The manuscript copies come from the estate of Franz Zwierzina. In Rosetti's time he served as second horn player, together with the first horn player Nagel, at the court of the Prince of Oettingen-Wallerstein. Most of the Rosetti concertos also originate from this court's collection of horn concertos, which includes works by various composers.
The concerto has come down to us as a set of parts in two versions, in F major as well as in E major. Both sets of parts (2 horns, 2 oboes, 2 violins, viola, basso) are identical in F major and E major. The solo horns, notated together, carry a note saying that the concerto may be performed in either F or E. The title page reads "Grand Concert" and names "Rossetti" as the composer. I do not agree with the assumption that these parts were actually played from: whole bars are missing from the individual parts due to copying errors, which would certainly have been corrected had they been used in performance.
What has unfortunately been overlooked or not properly taken into account so far is that a further set of parts exists for the first violin (F major) and for the two solo horns. These parts are written in a more spirited and less tidy hand. Above all, however, they probably form the source of the later copies. Numerous simplifications were entered in the solo parts, and some of the more difficult original passages were erased. This simpler version was adopted in the later copies. Whole bars with particularly virtuosic runs up to a notated d‴ were also struck out.
Fortunately, these deletions are still partly legible, so that both the solo parts and the missing tutti parts could be restored. This was not possible in every case, however: the second movement contains a section in the major, of which only the solo horn parts (partly) and fragments of the violin part remained legible in the copies. These 10 bars in total are printed as an appendix at the end of the second movement.
It can therefore be said with great probability that this concerto was originally conceived as considerably more difficult, that it was simplified for later performances and even transposed down a semitone. Was the concerto perhaps adapted to the declining abilities of the ageing Zwierzina and Nagel? An example can be found in Mozart's D major concerto: there, too, Mozart takes into account Leutgeb's age-related decline in ability, writing in D major rather than E-flat major and avoiding high notes. (This does not happen without Mozart's typical teasing remarks in the score, of course. The two must have been very fond of each other.)