Should Have vs Must Have?

"Should have" would mean that the person you are talking to did not tell you about the party, while "must have" would mean that the person you are talking to did tell you about the party.

Should have and must have difference?

Must and Should. Remember that must and have to can be used to talk about obligations. Should is different. You use should to give advice or express your opinion.

What is the difference between must and should?

Both "must" and "should" are model verbs. The term "must" is commonly used to express any unavoidable requirement or obligation. On the other hand, "should" is used as a probability, obligation, advice, recommendation, conditional, and exceptional mood.