The Hamlet Project

Serious question: How does the gravedigger know this is Yorick’s skull? I’m pretty sure he doesn’t have a preternatural ability to look at a skull and picture the face that once rested on it. So – does this mean that he is digging up Yorick’s grave? He’s already unearthed several skulls. Are they all in the same grave? That doesn’t seem logical. Also – why are they digging up graves? Is there a shortage of cemetery space in Denmark?
Is this three graves next to each other so he can tell who is buried in which? And to know, too, how long Yorick’s skull has been there. Is he looking at a gravestone? Or does a fool not warrant a gravestone?