From what I've read, in 1975, Jacques Sesiano in his Ph.D. thesis managed to translate four 'new' books from Diophantus' Arithmetica. This brings the total number of books of Arithmetica salvaged to 10 distinct books, if we include the 6 from Heath's Greek translation.

Does anyone know if any of the 6 Greek version of the books were found in Arabic? Has there been other major progress in finding the last 3 books?

Arithmeticahas been described as a collection so varied that, even after having read the solutions to a hundred problems, it is still hardly easier to solve the 101st problem. This is simply not true for the four 'new' books, for example the problems (and solutions) in the Arabic book known as 'Book IV' are all very similar to each other. It isn't true for Book I either, but this is after all the first book, and Diophantus has consciously arranged the work so as to progress from the easy to the difficult. $\endgroup$ – RP_ May 9 '17 at 23:00