Mcnaire, I never heard that Nanny actually wrote the "Dragonetti" Concerto. I was under the impression that he edited it. The concerto attributed to Dragonetti was likely to have been writen by someone else, but I'm not really sure if it was Nanny. Anyway, where did you hear that?
By the way, on a similar note, it is said that the 1st movement (and probably 3rd as well) of the Koussevitzky Concerto were written by a student of his, and then it was published under Koussevitzky's name. However, it is believed that Koussevitzky actually did write the 2nd movement, and there is an actual recording of him playing it somewhere out there in the world. I've never heard it though.....still looking.