I don't really have an opinion on whether or not the subspecies Rabdotus dealbatus neomexicanus should be recognized. Although I'm not very familiar with MolluscaBase, though, I'm not seeing anything there that indicates they believe Rabdotus dealbatus neomexicanus should be considered a synonym of Rabdotus dealbatus dealbatus. So I'm not sure what the rationale for merging the two is.

Oh, I missed the link for this and just searched MolluscaBase without success... so I wasn't sure if they even placed it as a synonym of Rabdotus dealbatus dealbatus. Odd that searching for "Rabdotus dealbatus neomexicanus" or "Rabdotus neomexicanus" on MB does not turn it up.

Yes it's because Rabdotus is a subgenus in that name and the searching gets funky with those.