Until today there is no evidence if Nanny or Dragonetti wrote the work. Nevertheless, we can compare the "Dragonetti concerto" to other Dragonetti compositions, like those recorded by Italian Ubaldo Fioravanti, works which don'y have the brilliance of our Nanny-Dragonetti concerto.
On the other hand, take Lorenzetti's Gavotte, which is so similar to
"Dragonetti's concerto" that I come to the conclusion that it was Edouard Nanny who wrote both.
That was also a commom practice at the time : it seemed more attractive to present a new work as a rediscovery. It's the case for
"Johann Christian Bach's viola concerto", in fact written by Casadesus.
Fritz Kreisler wrote inumerous "transcriptions", many of his own hand
and all excellent music.
The Eccles sonata is quite another problem : bassists think it was written for viola da gamba, while violists are sure it is original for viola
(I mean viola, not viola da gamba). Well, it is an original violin sonata.