All the control plane. Data plane is distributed and roles using iam to access resources can still do so during a control plane outage.
There were enough "surprisingly control-plane" IAM operations in the AWS services that I dealt with, so we had to exercise extreme caution during outages.
Even if I were the stupidest and least curious engineer around (and I was far from it), that's basically irrelevant to what you're scolding me for here…
As part of a team with both software development and operational responsibilities, like most teams at AWS, I had to deal not only with the consequences of my own imperfect knowledge, but also with the imperfect knowledge of my coworkers past and present.