A quick look at the RCC admittance profile in APOLLO indicates that RCC access is allowed as long as you're in C or F connecting to an International C or F flight. The example given is the following:

LAX/ORD C ORD/LHR C - OK

LAX/ORD Y ORD/LHR C - Not OK.

Of course it's always a crapshoot depending on who happens to be working the desk. If there's a disagreement, you can always refer them to the star, S*RCC/