Concerto No.3 D major for Horn, 2 Violins, Viola and Basso
(first print)
More hornist Willem Spandau (1741 - 1806) here by french horn.net:
This concert ROM 387 for Horn in D major comes from a copy of the music collection of Count Clam Gallas and is now under the signature XLII-A-9 in the National Museum of Prague - Czech Museum of Music kept.
It was for this edition make it clearly identifiable as numbered No.3. The concert seems much earlier than the two Parisian prints to have been around 1770, composed. It's more Clarin location and can not be compared with the 1st or 2nd concert.
Concerto No.3 D major
For this first edition, the Horn was additionally since edited as Corno da Caccia parts in B and as Corno in F.