When Mr. Krabs attempts to dig up the grave of Smitty, the stone shows his last name as "Werbenmanjensen." Earlier in the episode, Mr. Krabs lies to Spongebob and says that the owner of the soda drink hat belonged to Smitty WerbenJAGERmanjensen.
When Mr. Krabs thinks he's given up, he's standing by a gravestone. When he finds Smitty's gravestone before him, the other gravestone is gone.
In the flashback the hat had bubbles in it but there wasn't bubbles in when spongebob bought it.