So...we all were kind of confused when we saw in the 3rd film how Sandy met SpongeBob at Kamp Koral. Well, we later got an explanation for this in "Kitchen Sponge", where Sandy sent her past self to Kamp Koral to foil Plankton's plans. So...did SpongeBob grow up with Sandy at Kamp Koral? Does this mean their first meeting in "Tea at the Treedome" was a reunion? Well, yes, and no.
We have to think...Sandy SENT her past self to Kamp Koral. Which means a timeline exists where Sandy did NOT go to Kamp Koral with SpongeBob, also the original unaffected timeline. Therefore, the entirety of the Kamp Koral series occurs in an alternate timeline separate from the main timeline.