Dumbledore likely would have known what it meant, and I think Alastor at the very least would have put together the most crucial parts as well.
The part that was numb with grief and guilt took this opportunity to observe, speaking of obliviousness, that after events at Hogwarts had turned serious, they really really really REALLY should have reconsidered the decision made on First Thursday, at the behest of Professor McGonagall, not to tell Dumbledore about the sense of doom that Harry got around Professor Quirrell. It was true that Harry hadn’t been sure who to trust, there was a long stretch where it had seemed plausible that Dumbledore was the bad guy and Professor Quirrell the heroic opposition, but...
But did Quirrell know that Dumbledore would have realized? (I mean, there’s also a reasonable chance that Dumbledore was already well aware that Quirrel was Voldemort when he hired him but did it anyway, not least because if Voldemort was teaching Defense Against the Dark Arts he wasn’t going around leading Death Eaters and killing people.)
Dumbledore likely would have known what it meant, and I think Alastor at the very least would have put together the most crucial parts as well.
But did Quirrell know that Dumbledore would have realized? (I mean, there’s also a reasonable chance that Dumbledore was already well aware that Quirrel was Voldemort when he hired him but did it anyway, not least because if Voldemort was teaching Defense Against the Dark Arts he wasn’t going around leading Death Eaters and killing people.)