There are 2 different species of swallowtail angels being sold as masked swallowtail angels these days. Typically the more expensive Philippines ones are the "proper" Genicanthus semifasciatus. Lately in Indonesian shipments they have started labelling Genicanthus caudovittatus as masked swallowtails too.
Check carefully before you purchase.
Thanks. Appreciate the information. Building a fish list that is responsible, reasonably priced, LPS and predominantly soft coral friendly and ordinal is proving challenging Then trying to mix in fish that I've seen while diving in Hawaii, Japan, and around the Caribbean, well, means I'm living on this sub forum and reading