OK - nobody tackled this, Guido Braem and Sandy Ohlund really are the ones that should be handling this. I'll give it a go.
There is the widespread species that in its classic forms from Peru & Bolivia that is the type for Phrag caudatum. It is a big plant, big flowers which are basically green with lighter patterns and dark markings especially in the petals. In some the petal ends are fairly red. Pouch is green with some amount of brown on the outside. This is the classic caudatum.
. The name caudatum variety giganteum is a horticultural name that was not validly published. It was used as part of the sales pitch by 19th century dealers trying to distinguish the Peru-Boliva caudatum from the Colombian species that had smaller flowers and variously has been called caudatum, wallisii and last by Braem & Ohlund now called warscewiczianum. So the name giganteum is nomen nudum = a name with no meaning.
. The name caudatum variety sanderianum is another 19th cenutry sales pitch. The firm of George Sanders & Sons, used to add the variety name 'sanderianum' to any select clone of a species that came through their doors. THE NAME DOES NOT MEAN ALBINO. The firm Sander's used it the way Orchids by Hausermann would use "Addison" or "York" as clonal designation. It just so happened that many of the individual clones of albino Paphs the Sanders firm named 'Sanderianum' back when latinized cultivar names were allowed. But they also put that name on a few highly colored clones of some species. In the case of Phrag caudatum var. sanderianum the plant described in the Garden Chronicals matches the type description for the normal form of the Peru-Bolivia version of Phrag caudatum. In particular there was mention of the big green & gold flower with long petals with red petal tips. This again is typical of the Peru and Bolivia races of Phrag caudatum.
. So both names are not valid, they both refer to the typical form of Phrag caudatum. Use of these names has persisted because of the confusion between taxonomic variety and horticultural cultivar, especially when cultivars got latinized names this really confused the difference.
. that is what I believe is true, Sandy or Guido - correct me if I missed the mark, I did not hit the reference books.
Leo