In the beginning of the movie when Leonard is talking on the phone to the mysterious caller (who we find out is Teddy [John gamble {not thee John G}]). He says he is different from Sammy Jenkins because he faked his condition. So could you say that Leonard was Sammy Jenkins up until the part where Sammy's wife has given him the shots over and over. This is where it becomes Leonard's memory but he cant make new memories according to Anterograde amnesia. If Leonard had Anterograde these memories wouldn't exist. So how is it that he is able to formulate these memories after the incident and remember them as though they were before?
I am not trying to find holes in the story, I just found this interesting.