Don’t forget to add Gottleib Muffat (1690-1770) to the list of Handel’s sources:

http://home.telepath.com/~hrothgar/muffat_to_handel_c.html

There I rely on Sedley Taylor’s argument to establish Muffat’s priority:

http://books.google.com/books?id=F-oPAAAAYAAJ page 1ff.

Since Taylor’s 1906 book it has been found that Muffat’s Componimenti was advertised in the journal Wienerisches Diarium in 1739, indicating that it had already been published by then, or soon would be. This is right around the time that Chrysander and other scholars have surmised, and well before Handel began work on Theodora.

http://books.google.com/books?id=XxDisZxtRBcC&pg=PA90