1851 to 1885 --- heck a 34 year age range is what most folks would call "close"--- now if found along with those coins * used them to assist -- if it was found together with the coins with the half dollar being dated 1876 it had to be "lost "after 1876 *=---so now the question then is how long did he owner have it in his pocket before losing it ? anytime from 1851 to 1885 since half dollar coin in the pocket "spill" of this was one is dated 1876 it wasn't lost before to then of course.
these 3 items if found together had to be lost after 1876 * since the lasest coin date is the half dollar dated 1876:* now the knife was made up until 1885 * so it possible with this pairing any time from 1876 * or later on this " pocket spill" was "possible" but not before that.