I do not know how one can distinguish with certainty between knives and scrapers, except when the latter are so blunted that they would not readily cut. I suspect that we tend to call an artifact a knife when it is roughly long and narrow, or when its business edge runs lengthwise, or when its shape suggests that it was hafted. Any of these is inadequate basis for identification; scrapers could be hafted, and knives were not necessarily so. I would suppose that any tool that cuts like a knife could also be used as a scraper, although not always vice versa.