This James Mackay worked for the Spanish in Missouri. I think if you google his name you will find out a lot more about him. I know two members of his family have now completed books on him. His map was used by Lewis and Clark to start their first journey of discovery.The other James Mackay was at Fort Necessity with George Washington. There is an account of him in the Washington presidential libray.Unfortunately James tried to visit Washington when he achieved the presidency bu unfortunately he died on the way. I did an extensive family search and found that Don diego has nothing to do with my family. Maybe on his Macdonald side. The Macdonalds were our neighbours at Milton just up the road from our farm, Frobost in south Uist. I am reliably informed that Flora Macdonalds step father's mother was Catherine Mac Kay You could also try the London Gazette archive which is on line. It gives dates of commissions etc.with regiments.