Yikes!! The usage in the title is just plain wrong, but such an easy mistake to make because of how the phrases SOUND. If you just listen to each phrase, it would seem “could of,” “should of,” “would of,” and “must of” are correct. However, the proper usage is actually:
could have – should have – would have – must have
OR the contractions of these phrases…
could’ve – should’ve – would’ve – must’ve
Just goes to show you…you can’t always trust your ears when it comes to spelling & grammar!