No, you're misunderstanding it. See, people remember Mark, alive. They also remember that a guy was killed at the Pokémon Festival. It's the connection that is buried deeper - his parents don't really remember that it was Mark who died there, and the unconnected people who read about the death and meet him later don't realize that his name and appearance are the same as the guy who was killed, unless they see direct, undeniable evidence, such as in Crater Town where people could look at the newspaper article about his death and him alive side by side.
Mark: Eh? That was a joke. o_O
May (again): What, should one have a problem with being named after a month?