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HankronI guess that may be a little confusing when looking at an online images, as the little guys often have various designs as part of the photographic print that look like a the border of a mount. So I change it to that the main difference is that, other than the player images, the N172s and N173s don't look like each other.
One quick aside: other than those little trading cards and some abnormally large examples (i.e. 15x15" or larger), almost all untrimmed 19th century albumen photographs will have the photographic print affixed to a larger mount (you can see the borders of the mount surrounding the photo). And, due to the thinness of the paper used at the time, almost all Pre-1895 albumen photographs had to be mounted to something-- though in some cases a photographic print might have been mounted in a book or on a scorecard, rather than a sheet of cardboard. So, as a collector, one of the first things you look for is how that 1880 photograph is mounted, because, unless it was skinned or otherwise removed, it has to be pasted to something substantial.