Josuke suddenly steals Jotaro's pen and Jotaro's like "I'll pretend this never happened". He used to be more perceptive!
I guess that's the fate of the protagonist of the previous Part, gotta let the new hero shine.
Jotaro hasn't been using Star Platinum's timestop for 10 years but everyone knows he can do that. This is why DIO was staying put in his mansion, if he ever stepped out of it the Crusaders would immediately learn The World's ability.
So Polnareff's fingers grew back.
Also, since reading this part (watched anime first) I kinda thought that the reason DIO's face is always in shadow is to