The plot revolves around Adam trying to see Porky's in theaters, which was in theaters in 1981. Also in the episode Adam mentions Field of Dreams which came out in 1989.
The opening montage is supposed to show Adam purchasing movie tickets on different occasions (he is wearing a different shirt each time), yet the same girl wearing the same outfit is standing in line behind him on what are supposed to be two different days.
The plot involves Adam having to sneak into Porky's because it is rated R, but the early montage shows him purchasing a ticket to The Lost Boys, which was also rated R.
Barry makes a reference to the movie Field of Dreams which premiered on 05 May 1989. He couldn't have know the details of the movie around Valentine's Day 1980 something.