I tuned into "The Simpsons" last night and enjoyed my trip back to the 90s. The story covered a period of time after Homer and Marge graduated high school but before Bart was born. It sent up 90s stuff like grunge and cigar bars. Homer's grunge songs were actually pretty sweet, mimicking Nirvana's "Rape Me" and Bush's "Glycerine".
Any fan of "The Simpsons" has accepted the flexible reality of Springfield. On this show it's okay to violate laws of consistency for the sake of a joke. For example, if an episode calls for the Springfield Nuclear Power Plant parking lot to be visible from the Simpsons' house, that's how it will be for one shot, and that's okay.
Last night's episode, entitled "That 90s Show", wasn't just a piece of flexible reality, it was absurd. We all know the story of Bart's birth and yesterday's episode just doesn't fit the puzzle. Weren't the 1984 Olympics taking place when Lisa said her first word?
On preview, it doesn't matter. They can blow away the space-time continuum so long as it results in a good episode.