I do often wonder if Green Nephthea really are nearly extinct in the wild, or if it is just a sales pitch given by the aquaculture facilities that sell them. Either way, with these corals, extinction in the wild doesn't translate into rare. It more of comes down to identification and we all know how good LFS's, or even online stores, are at that.
Since telling them apart can be quite a chore, even for people who know exactly what they are looking for, it really doesn't matter from the retailer's perspective. The prices are similar either way so there isn't much incentive to identify past "Green Finger Leather". If it's is small and bright green, it is labeled "Rare Green Nephthea". If it is big, "Green Sinularia" or "Neon Green Finger Leather".
A similar thing happens with Colts and Kenyas with the purple tree corals. And those are easier to tell apart.