Most information I have on the RCA COSMAC Computer Game System is based on Andy Modla's work as documented on his github page: RCA Studio II and Studio III Home TV Programmer.
As Andy mentions on his page:
The RCA COSMAC Computer Game System is based on the FRED II computer and uses the CDP1801 microprocessor. It read tapes to load game programs. The Hagley Library Acc. 2464, Box 919, FRED folder 4, has a document written by Joe Weisbecker in January 1975 titled "Instructions for the RCA COSMAC Computer Game System". I conclude that the games described in the document were written in the late 1974.
