Richard Owen publicly described the type species of Diictodon, D. feliceps, in 1876 in a book titled "Descriptive and illustrated catalogue of the fossil Reptilia of South Africa in the collection of the British Museum." In its eighty eight pages this book also described and named other animals in the collections, but for the first time Diictodon was shared with the non-scientific community in an official capacity. Diictodon isn't on display these days (I can't find a record of it being on display at least and it may not have been in Owen's day either), but I'm more than certain that in its expansive storage the British Museum (along with a number of American museums to be sure) has more than one specimen.
Some of the other dates for naming of species within the genus are Diictodon galeops (Broom 1913), Diictodon grimbeeki (Broom, 1935), Diictodon ictidops (Broom 1913), Diictodon palustris (Broom 1913), Diictodon psittacops (Broom, 1912), Diictodon parringtoni (Von Heune 1942), and Diictodon tienshanensis (Sun 1973). This last entry does not appear on the encyclopedia's list of species but after being described by Sun as an Asian Dicynodon it was renamed a Diictodon by Culver and Hotton in 1977 and 1981 papers.
Robert Broom's extensive work with Diictodon was thanks to his being an ethnically Scottish South African which means he lived where a lot of the fossils of this animal have been found in Karoo formation of South Africa.
Friedrich von Huene was the German version in the 20th century of the 19th century Briton Richard Owen. He named more animals in his life than anyone else in the 20th century. He was born in Wurttemburg before it was even part of Germany! His career spanned the ages of fossils and he was a jack of all eras, not really sticking to any specific time period.
I'll keep looking for info on A. Sun. It is very hard to find information on Chinese paleontologists!