The sources of this concerto for two solo horns and orchestra are quite complicate. The copies were found in the posthumous works of Franz Zwierzinas, who was a second hornist and played together with the first hornist Nagel at the Court of Prince Oettingen - Wallerstein at the time of Rosetti. The prince collected horn concerti of several composers, among them Rosetti.
This concerto had survived in two complete versions, one in f major and the other in e major, and some additional parts for the solo horns and the first violin.
The versions in F and E major are identical (2 horns, 2 oboes, 2 violins, viola, basso). The two solo horns, written together in one part, were to be played in F as well as in E. The title says "Grand Concert" composed by "Rosetti". They is an assumption, that these parts were used in concert, but I have to oppose that there are several bars missing. If these music sheets were used for playing, the mistakes were probably be corrected.
The interesting part of the sources are the additional parts of the first violin (f major) and the two horns. These notes are rather fluently written and less neat. It seems to be the case that this version was the basis for the other complete versions. It is still readable that the solo part was simplified and difficult music passages were rubbed out. Complete bars with virtuoso scales to d''' were crossed out. Fortunately, the original version is still readable under the corrections. In most cases, the new edition follows this original text which can be seen as the composed version by Rosetti. There is one passage in the second movement, a major passage, that could not be completely reconstructed. These ten bars are to by found in the appendix of the second movement.
According to the sources it is to be assumed that the original composition was more difficult and virtuoso than the later copies and the simplified version in f major. Is there the possibility, that the concerto was simplified for the older horn players Zwirzina and Nagel? One example for this praxis is found in Mozart's concerto D Major, which was written for the older horn player Leutgeb and thus not in E flat-major and without many high tones. (This was of course not written without teasing notes by the composer for Leutgeb. They seemed to be really good friend.)
The last point to be mentioned is the strange fact that there is written a rondo movement after the third movement, which was composed by Feldmayr (chapel master and successor of Rosetti) as third movement of a concerto for 2 horns. The reason could be that the concerto for two horns was to be meant a bit longer so that this movement was added although there is no connection in musical contents.
