I couldn't find specific scenario related this case in RFC 4006(Obsolate). They have made it clear in latest RFC 8506.
For example I granted quota for rating group 0 and 1(CCA-I). Now gateway reports used quota(CCR-U) for rating group 0. Should I send(CCA-U) all available quota again in answer or should I send the one that got reported along with requested service units for different rating group?
At this point I am sending all the available rating groups in CCA-U
Always respond to the Rating Groups which were requested.
I don't have a reference to the RFC but below a dump from a real-life flow. See CCA's containing only RGs which were listed in the CCR's: