In fact, that's the only way to get Merlinus' A supports with Nino and Vaida. Getting a C in CoD is easy enough, but the problem is afterwards because Merlinus can't be deployed in the next map (the Durandal/Armads map) and the two maps (Sands of Time and Battle Preparations) after that have time limits. You have to oversupport in CoD so that you can get the B in Sands/Battle Prep, and then finally finish with an A in VoD/VoL (it must be finished there because no Merlinus in Light).