We've covered the situation of discrepancies in the end credits of a TV episode in the past, when the name of the character doesn't match what we heard within the show. The three episodes we have in this file so far:
Ann Maxwell in credits
Ann Martin in show
CURB YOUR ENTHUSIASM
Dr. Salvin in credits
Dr. Slavin in show
Joshua Wheeler in credits
Joshua Donovan in show
The Toobworld Central policy is to ignore the credits. What happens within the show is what happens within the "reality" of Toobworld. But there was a recent end credit discrepancy that was too intriguing to ignore....
In a recent episode of 'Merlin', the character of Arthur Pendragon was accredited to two different actors in the end credits. Bradley James was first named as the future king, which is who actually plays him. But then the role was attributed to Richard Wilson as well. Wilson appears in the series, but he plays Gaius, Camelot's court physician and mentor to Merlin in the secret tutelage of his magical powers. Being the madman I am, who sees possible plot twists where they don't exist, I imagined that Gaius was in fact Arthur as an old man who had gone back in time (via magic, of course - unless he hitched a ride on the TARDIS!) in order to make sure Merlin would be around to protect him in the future. Since the series "Merlin" takes so many liberties with the established legend, perhaps in this alternate TV dimension Arthur does survive into his dotage.
But falling on Occam's Razor, it's far simpler to just follow the standard rule and ignore the end credits......