Hi Clint
Thanks to the seller, we cannot be 100% certain exactly what the fourth digit is in the true serial number.
Neither can I explain the Italian "habit" now and then to add an extra digit out of line, as here, with a digit 1. Seems they try to tell us the type number I suppose
Anyway it looks to me as if the Italians used the Nieuport 10 as a kind of advanced trainer and it was ordered in many batches, one of which I have stated as Ni 13358 to Ni 13469.
This of course compromises Hd 13358 to Hd 13400....but the photo is not of any HD.1 is it?
Cheers
Stig