I think in time of war, especially the early American Wars, not every soldier was kept accounted for.So info on some may be found, and not found on others.So I really can't answer your question.
I do wonder though about the "Samuel Cobourn" listed in the 1810 census for Floyd County, Kentucky.In the 1850 census for Floyd you find a younger Samuel Cobourn - born 1783, and you find Jeremiah Cobourn - born 1774.Could the older Samuel Cobourn of 1810 be Jeremiah's father??This Samuel Cobourn is listed to be "over 45 years old".So in 1850 he would have had to be at least - 85 years old.
Since Jeremiah Cobourn is listed in the 1810 census for Giles County - and possibly enlisted in the War of 1812 in Virginia, this might be why his family was not mentioned.They may have been living in Floyd County, Kentucky. (Just speculation - more research is needed).