[Listener]

Hello. Let me join you!!

Your arguments are confusing because you are not distinguishing "the time of the event" and "the time of the judgment." What's complicating is that both events and judgments can have probability.

"Can have + past participle" construction refers to "present probable judgment on a past fixed event."

Example: We can have used the bus instead of the train. (Both were possible; actually the train was used.)

"Could have + past participle" construction can refer both (1)"present possible judgment on a past fixed event," and (2)"present fixed judgment on a past probable/possible event."

Example (1): The child in a pretty dress we saw yesterday could have been a boy.(Actually one of the two was true; still not completely sure which was.)

Example (2): You could have been killed in yesterday's accident. (There was a possibility but actually it did not happen.)

My analysis may not be complete, but the point is that the event and the judgment must be distinguished.