Obviously you can't be 100% sure, but I think senegals are a perfect example, that sometimes you have to use some reasoning. The difference between WC and CB depends IMO on the species. Some like senegals very rarely achieve larger sizes or don't have other characteristics that WCs have (long slender, other unexplainable traits). And some like Teugelsi you can tell pretty easy whether it's CB or WC, by it's pattern. The CB teugelsi that are coming out have a unique pattern to them. Other key variables come into play when determining weather a poly is CB or WC like where you get it, for some at what size you get it, and for other at what price. It really depends on the individual case. As far as some more characteristics CB endlis have more of a short rounded head with frog eyes (most do at least), while WC have a longer head with more natural eye placement.
so besides the size difference there are some differences that to me stand out. One is the pattern. If you look at your teugelsi compared to the teugelsi on the left (CB) they have a very similar pattern. While their base colors may not look very similar they are on different tank bottoms. Another key difference I have noticed between the CB teugelsi is the lack of an elongated flatter head. It it noticeably more round than it's WC counter part. Lastly it's tail is almost rounded compared to the WC teugelsi. It is more oval like compared to where the WC teugelsi's tail keeps going until it meets the bottom making close to a curved V. (These pictures are not mine and I do not take credit for them)
