I think one reason for the Capt. on his tombstone could be the late date that the stone was placed.
I have a copy of a letter that was placed on the Auchmuty Gen Forum Mar 5,2010 by Ruth Spencer stating;
"My grandmother ,Mrs, Mae Guinter, mother, Mrs. Ann Leidhecker and myself had the maker for Captain Samuel Auchmuty Sr. placed by the Veterans Administration Aug.20 1989 in the Old River Cemetery, Fishers Ferry, PA. The grave marking was verified by the Veterans Admin. and Lycoming Chapter DAR of which we are members. Capt. Auchmuty is our direct Rev.Ancestor." End.
I also have heard of persons using the address 'Capt' as a title for older military men. Also as a term for a leader or head of an organization. My father who passed away in 1960 often used it as a form of respect o coal mine boss. I can send you a copy of the letter if you send me your e mail address. my email is prpm2@verizon.net. Samuel is also an Ancestor of mine.-Patrick Morrison