Ok, a couple things here...i agree with you on one point and disagree on another. You can't simply go by scientific name for multiple reasons. Two that instantly come to mind are the fact that corals are incredibly difficult to identify at the species level. Furthermore, as you pointed out, these are color morphs/genetic variations among the same species which are given different names (in the scientific community this is referred to as phenotypic plasticity).
Where i disagree is where you say that there should be some sort of registry. Vendors do not want that. That would make it impossible for them to come up with absurd slight variations and claim them by a new made up name.
Lastly, in regards to the natural geographical distribution, while i see what you're getting at i have to partially disagree about how relevant that really is after many years in captivity. This is partly why so many people try to avoid maricultured corals and wild collected corals (they have differing requirements in regards to both water and light parameters).
I hear you on the vendors.
The registry is just a pipe dream for me. I have been trying to collect different strains of GSP but often see the same ones labeled under different names. It would be helpful to have a go-to online registry with submitted information that we as a hobby have collected that includes genus name, AKAs, vendors that may carry that coral, etc.
The point I made about noting where a coral was collected isn't for cultural requirements, but more about identification. If we can figure out that the Weeping Willow was collected a far distance from other long-polyp toadstools, then it would help support whether these corals are genetically distinct. As in they are not fragmented from each other or come from the same colony. Thus it would be fair to classify them under two different trade names.