Is Leonard's Last Name in Memento Really "Shelby"?

Writer's Note: Do not read if you haven't seen Memento. This post contains spoilers.

So I recently watched Memento and I will admit, even though it was my second time watching it, I was still very confused on the ending. I guess that would be a good thing. But while I was watching it, I caught a bit of the credits. And I realized that Leonard's last name is not given in the ending. If you don't believe me here' the picture:

As you can see, Guy Pearce does not play someone named Leonard Shelby, but is credited as someone who simply plays Leonard. Now this could just be for simplicity because no one else has a last name. For example, Sammy Jankis is credited as only Sammy. Now this is a purely wacky idea, but what if Leonard was wrong about his last name? It really doesn't make sense to some people because he told other people that his last name was Shelby and no one corrected him. In fact when he told Teddy that he is Leonard Shelby, Teddy responded that that was who Leonard was. But there are only two people in the entire movie who refer to Leonard's last name. One of them is Leonard himself. The other is Mrs. Jankis, who we know is SPOILER a figment of Leonard's imagination. So Leonard is really the only person who refers to his last name. This begs the question: was Shelby really Leonard's last name? It probably was, but with these two new pieces of evidence, it hopefully kinda makes you wonder.