At some point I read an article or a transcript of an interview with an Intel employee (or former employee) who had been involved with the design of the 8085, describing how he had specified additional instructions over those of the 8080, and they had been implemented in the silicon, but then the decision was made to not document any of the new instructions other than RIM and SIM.
I no longer recall which Intel employee that was, and can't find the article or interview. Does anyone else remember that, and perhaps have a copy? Eric