Essentially none of the Legacy entries are registered, nor are they likely to be unless something changes at the International Aroid Society, the registration authority for most Araceae genera. Many stable forms of various Aroid genera/species, including those you've mentioned, are not registered. These primarily fall into two categories, those which are stable forms and those which are currently considered synonyms of other species.
Elephant's Ear (Alocasia zebrina 'Tigrina Superba') and
Elephant's Ear (Alocasia zebrina 'Reticulata') fall into the former category. Most of the plants in this category are collected plants. Some believe these are actually different species but I don't believe genetic level studies have been conducted.
The second group of Aroids includes Alocasia macrorrhizos, Colocasia esculenta, Xanthosoma sagitiifolium and others. Theses species have been in cultivation for so long that, according to the botanists, definitively wild populations of the type plants are unknown. "Further study is required" is a common (para)phrase in many of these studies. Some of the synonyms of these species you will find in our database as accepted names or as cultivars. and are examples in our database.
I've found comments by Alistair Hay, Thomas Croat and Peter Boyce supporting these types of usages and encouraging people to submit these names for formal registration.
African Mask (Alocasia 'Amazonica') and
African Mask (Alocasia 'Polly') are slightly different examples of plants that aren't formally registered but are included in our database. As you probably know A. x amazonica is a hybrid bred at the Amazon Nursery in Florida and never formally registered. A. 'Polly' is a tissue culture selection of A. x amazonica with shorter petioles and generally more compact habit. It was selected by one of the Rotolante brothers but I can't remember which one. Because both are common, named varieties, I've chosen to include them in our database as well, even though they've never been registered.
