Good questions ! I am not a professional archaeologist either, but I spent 3 nights this month in a Holiday Inn Express, which counts for something in some circles. I have been interested in the timeline for bow & arrow introduction, or invention, in the Americas for a while myself, and ToddsPoint's info is the first real info I have heard on the subject in my casual observation. I would be curious in knowing how it was determined that the points found within the profiles of the skeletons were deemed to be from arrows, rather than from darts, spears, or knives, perhaps some thin wood ends of arrows still remained with the points?
I find the 400-500 AD dating particularly interesting because it seems to correspond with some of the dates I have seen regarding the introduction of Jack Reef points, which some researchers seem to be thinking originated in the Newfoundland area of Canada. I have wondered if perhaps an early appearance of Scandinavians in that area of Canada might have been how and where bow & arrow technology was introduced to the Americas? I saw somewhere some images of roughly 500 AD metal arrow points from Scandinavia that reminded me of the profile of Jacks Reef points, but then again a lot of much earlier American lithic points have very similar profiles.
I also suspect that the early east coast contact period accounts of the points witnessed on arrows being triangular, and subsequent digs dating triangular points to the middle and late-middle woodland period, had resulted in a consensus that triangular points=arrow points, and thus arrows were introduced when triangular points were.