Good question. It is possible that SpongeBob has a copy of each of his employee of the month awards and there are copies of them at the Krusty Krab. I'm not sure, but it is the only possible explanation that I can think of.
Well, the awards were shown again in the Krusty Krab in The Original Fry Cook.
However, it is possible that The Original Fry Cook took place before the movie.
The movie was set after the series