past tense - "Why couldn't" vs. "why couldn't you have"


Reading Harry Potter 2, I came across the following, and I wonder if the use of couldn't have is the equivalent of couldn't in this context?



"I have got a question, Oliver," said George, who had woken with a start. "Why couldn't you have told us all this yesterday when we were all awake?"



If we change it to the following, how does it change the meaning of it?



"I have got a question, Oliver," said George, who had woken with a start. "Why couldn't you tell us all this yesterday when we were all awake?"



And what is the difference between the following?



If you couldn't do it, you should have told us yesterday.


If you couldn't have done it, you should have told us yesterday.





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