In conversation with 2 native German speakers I said,
Ich dachte, dass Sie mir gerade erklärt haben, dass sie der Rundfunk verwandt haben.
and they corrected me to:
Ich dachte, Sie hätten mir gerade erklärt, dass sie den Rundfunk verwandt haben.
I would like to understand why the change. According to Hammer's German Grammar Konjunktiv II is used to express a remotely-possible condition -- "something which typically did not come about." But the sentence given is attempting to confirm a condition that is thought to have actually occurred.
Of note, this post does not answer why this usage appears to me to be outside of that proscribed by Hammer's Grammar, so is not a duplicate.