Apparently, the Nevus of Ota matches the characteristics of Elly’s birthmark much more closely than the Mongolian Spot. (From what I've gathered) not only do the colors seem to match better, but the former is known to persist into adulthood more commonly than the latter.

I don’t really care to fuss about specifics or anything–looking around, there were a bunch of names for a bunch of very similar things--it just felt like something interesting to share. Just some updated perspective on my end. Seems like some circles have been using the terms interchangeably.