Interesting question, but I think you mean to say:
Is there any difference between the following sentences?
Since no context is given I can only speculate about what the intent might be, but I can think of a possible usage.
Bob: Sam told me all about what happened.
Bert: He couldn't have told you anything. He's in a coma.
As for the other one, perhaps:
He should have done his homework and not left if for me.
(I don't know how you would use "leave" there.)
Student or Learner