On the one hand, R (http://www.cs.bell-labs.com/who/dmr/index.html) is sadly gone. However, this might be interesting to your question:

From http://www.lysator.liu.se/c/duffs-device.html:

"Somewhere I have a note from dmr [the R in K&R] certifying that all the compilers that he believes in accept it."

So at least at some point Duff showed Ritchie something in C that Ritchie hadn't seen or considered before, long after C had been invented.