The Royal Wedding was July 29, 1981 but "Eternal Flame" was a song by the Bangles from their 1988 album "Everything" and became a hit later in 1989.
The wedding of Prince Charles and Lady Diana inspires Beverly to renew her and Murray's wedding vows. Barry and Adam form a rock band. Adam, sitting behind his drum kit in his family's living room, auditions for a gig at the re-wedding wearing a Spinal Tap t-shirt. The Royal Wedding took place on July 29, 1981; This Is Spinal Tap was released in 1984. A goof, unless the character Adam lives in the same universe as Spinal Tap, who released their first album in 1967 and were filmed on tour in 1982 for Marty DiBergi's documentary.
Murray gets home at "6 pm sharp" and sits down for dinner. A grandfather clock behind him shows it is 7 pm. But the pendulum isn't moving, so the clock is stopped. That would explain the incorrect time.
Barry wears a Bo Knows t-shirt. The Nike ad campaign for Bo Jackson first appeared in 1989.
The Twisted Sister song "We're Not Gonna Take It" was released in 1984, but this episode is pinned to the wedding of Prince Charles and Diana in July 1981.
The movie posters in Adam's bedroom ("Back to the Future" [1985] and "Short Circuit 2" [1988]) both relate to movies that came out years after the wedding of Prince Charles and Diana in July 1981.
Princess Diana was called the people's princess after her divorce from Prince Charles in 1996.