IM built 200 Speedster with a price of $15,000 by the end of 1977 according to Andrew McCabe/Paula Reisner's book INTERMECCANICA: The Story of the Prancing Bull. The book says the Roadster/Convertible D body was developed in 1978 - it was later called the Roadster RS in 1981.
I suspect the Sports/convertible class was probably something enter by DMV in titling the car at one time --- since it was based on a plain Jane VW Bug Sedan in most instances.