A big thank you to Christina Karlsson of Sweden for digging into my question about where the white Bella came from and getting the answers. Also, a thank you to Julie Kennedy for contacting Christina in the first place.
The collection number was assigned by Surisa Somadee, and the PES comes from the name of the collector Dr. Piyakaset Ek Suksathan. This is the same collector who found Hoya lithophytica formally known as Hoya sp. Umphang PES01. The plant was likely collected in Thailand and given to Surisa in 2007.
The fact that there is so little of this wonderful plant in the trade after 11 years, I think, is a testament to the difficulty in its propagation.