I think the expectation is that it's OK to send corrections without support being known (MUC etc.), as the body itself acts as a correction even without support and no extra stanzas are involved (you're going to be sending the correction one way or the other anyway), but that it'd be smart to tell the sending user that support isn't know. I'll add some text, ta.
I'd note that the same rationale applies to the (silly) muc service replacing the id. No harm, simply works better with services that don't behave like this.
