If I remember right early brass tacks were one piece, all brass with a square shank, some with a little swell and the heads formed flat, domed, diamond, etc… no hollow in the head. I imagine the ones we use today came about some time during the Industrial Revolution (circa 1760-1850?), I would bet these are machine made. Could have been added anytime during the horns life.
Tacks, how early…not sure but I have seen them on Colonial furniture, trunks and tack that have been documented.
Here is a link to a source I have used scroll down the page and you will see nail and tacks:
http://www.thetrunkshoppe.com/ Tim C.
PS: Thanks B.TC