"would have v3" or "must have v3" for guessing about situations or things in the past

Question

We were taught at school that condition 3 (would+have+v3) is used for unreal past, which means "there is no more chance for it to happen in the other way around" such as "if you had driven the car carefully, he would not have died". So, we can easily understand that "condition 3" is used there is no more opportunity for something to happen in another way because it already happened in the past. You can't reverse the time.

But today, I was watching ITV and the TV presenter, when he appeared after a break, said:

"If you were watching earlier, you would have heard me talk about the solution."

He simply referred to his previous talk about a solution before the break. And the break-time passed. So he appeared again and he continued talking on the same issue. So he wanted to remind the viewers that he was talking about this issue before the break time.

But I got confused when I heard him said ""if you were watching earlier, you would have heard me talk about the solution." He used conditional 3 (would have v3) which seemed irrelevant to the situation, as in this situation he is not referring to a past event which he now wishes to have happened in the opposite way.

What he is doing is to guess something did happen. So, the situation here is not a wish for past event, and it is only a guess or assumption about a past event.

So;

1. Why did TV presenter say "if you were......., you would have heard me..."? instead of "If you had watched ........"
2. Would it not have been better if he instead said "....you must have heard me...", not "would have heard" because he is guessing or assuming that something was highly likely the case. And "must" is the right word, for highly likelihood.

Answer 1

The so called 3rd conditional would be the following:

If you had been watching earlier you would have heard me talk about the solution"

If + Past Perfect (and) Would/Wouldn't have + Past Participle

This means a viewer who was not watching before the commercial break cannot go back in time to hear the presenter talking about the solution.

The speaker in the OP's case is suggesting that there are some viewers who may have just joined the show, i.e after the commercial break.

If you were watching...

The phrase uttered by the presenter is perfectly grammatical (some English grammars call it mixed conditional) and is not ambiguous at all.

From Google Books another example:

It was then, if you were listening closely, that you would have heard Will whisper ever so softly to Madeline, “Is it too soon to ask you to revisit Savannah with me, my dear?”