They're not always under the same MCC ID.
I understand that we can use tools like aw-reporting (i've contributed multiple fixes and improvements to that project), and utilize it's multi-threading, etc.
However, this isn't always the best way to do this. I've got a more "real-time" use for that functionality in a web environment, so utilizing PHP would be more likely used for this request.
That being said, I know I can thread out these requests one at a time, which puts more load everywhere. The situations where the MCC IDs are different, the ability to submit an array of authorized CIDs to the reporting interface would be highly preferred.