The difference between atlatl dart points and arrow points isn't size, it's time. I have Palmer, Lecroy, etc. dart points that are close to 10,000 years old and are tiny-smaller than 90% of the arrowheads I make for my own use. Some were big, some were small, many were problaby knives or other tools. The only true test as what it was is to type it to time frame. Most points before about 1,000 BC were dart points or knives, after that, more and more arrow points started appearing as the bow's use spread.