The man (Bill from Maspeth) just told you that the R27s operated on the "C". He even stated that he himself drove, not rode, but drove the R27 in regular "C" service. I stated that the "C" train, loaded with R27s ran right past my house, which means I get to observe this first hand, seven days a week.
What is it going to take for you to understand that just because you didn't observe R27s on the "C" train does not mean that they did not run in regular service on that line?
I really hope that your friend, Larry Redbird R33 has accurate car assignments from the times that I stated so you could see that the R27s did indeed run on the "C" train.