Adam and Emmy argue about who is Goose and who is Maverick and later that evening his father gets angry because his wife and daughter are being noisy and arguing while he is trying to watch That's Incredible. Top Gun came out in 1986 and That's Incredible ended its run 1984.
Again, see the Goofs for the entire series. Things from all parts of the 1980s were intentionally placed anywhere by the series creator, hence why he says "Ninteen-eighty-something" at the beginning of every show.
When Harry Met Sally... (1989) wasn't released until 1989. This would make it impossible for Adam to invite Emmy downstairs to watch it on VHS tape or on TV. They would have had to go to the movie theaters in the 1980's to see this.
When Harry Met Sally was released to theaters in July 1989, which meant it was out in the video stores by the fall of that year at worst, making it entirely possible that the movie could be watched at home in the 80s still.
The narrator gives the sate as being in February, but the weather outside throughout the episode is more appropriate to spring or summer in Pennsylvania. Adam and Emmy are seen riding their bikes down the street without coats or jackets, and Erica goes to a toga party in only a sheet...and nothing else.