I infer from the context that ZGEN is defining cEVR as the intersection of RVR and EVR, i.e. undetectable virus at both 4 weeks and 12 weeks.
I believe it is no more complicated than is written - EVR as defined by viral load below 50 - and the c just specifies that it is NOT an EVR according to a different definition such as >2 log reduction. I.e. in order to use a standardized definition instead of 'undetectable' which is a target that moves as the assay technology improves.
And note that that is consistent with usage elsewhere on the web.
"I infer from the context that ZGEN is defining cEVR as the intersection of RVR and EVR, i.e. undetectable virus at both 4 weeks and 12 weeks"
I don't - if anything the use of the term cEVR implies they are not including RVR in the definition, since subdividing EVRs into complete and partial (> 2 log drop at 12 weeks but not undetectable) emerged to help prognosticate SVRs specifically in situations where RVR was not achieved of course someone can contact the company to clarify, but my guess if RVR is a separate secondary endpoint