Winchesters of the late 1800's had serial numbers, tho the dating of those numbers is more an art than a science. The first serials were very lightly done so with normal use they would wear off or become unreadable, but in the very early 1890's they started stamping the serials deeper.
All the Winchester made replicas of the 1886 were small quantity limited edition runs of 1000 or less with special serial numbers for those guns, all sn's started at 001, 0001 or x001 in the replica's. The reciever would be the easiest way to tell, these guns were case colored while the replicas are case colored also it would be much duller and worn on an origional. most older gentlemen who grew up in the early 1920 or 30's could tell you if it's circa 1900 case color or repro.
They did a run of 500 guns in the 1886 take down model in 45-90 a few years back.