Purchased this arrow a while back. Thought it would look good in my display. Don't know much about it but it was priced to sell and looks hand made with some good workmanship.
There is one sure fire way of determining if it is a modern knock off but it would involve untying any portion of the sinew wrapping, just enough to touch a lighter flame off on the sinew end, if it "balls up" and melts then it is an artificial sinew, if it burns to ash and smells like hair burning then it is real animal sinew.
I still make our Tribes arrows for ceremonies and I see a few red flags on your find,
1) The feather fletching's would have long ago been rotted off or consumed by insects.
2) the shaft appears to be "Carved" we draw our arrow shafts through sharpened holes in a flat piece of bone which gets them round and we wouldn't have, slice marks in the shafts, our arrows are a sense of pride as well.
3) I see no evidence of a blood groove in the shaft, these are cut into one or two sides of the entire shaft so that when it enters flesh the quarry will bleed out quicker. (the blood grooves are gouged in place using the same bone tool),picture a very sharp "Pac Man" shaped hole cut through a flat bone, we draw the reed or branch through this and the hanging point (Pac mans mouth) cuts the groove as we form the shaft.
There are many more steps but you get the picture.
I'll be happy to answer any Native American questions on this forum if I can, Be Well, J. Red Horse