I think the one most important factor to consider is that the inlay of a true C&S chip be a "litho inlay" and not just any inlay of paper, metal or clay (same composition of whole slug) even though those inlays can be smooth/flush and, such as Robert mentions; sealed.

I always believed the "crest" portion of the manufacturer/distributor term Crest and Seal chip meant it was comprised of a litho inlay.