Definitely mid-19th century (circa 1850's-1860's) rosette from horse furniture*.
(*meaning equipment, rather than an equine recliner

).
Creskol (the first to reply to your earlier inquiry), posted a link to a nearly identical rosette shown in Western & Eastern Treasures magazine, in the Ask Mark Parker column. Was that overlooked in your "all over the Internet" search?
This style of rosette is made of a thin sheet of rolled brass, stamped with a design, and filled with lead solder in the back. Originally there would have been wire attachment loops of brass, copper, or steel, imbedded into the lead solder back, and extending out to affix this to leather.
CC Hunter