At the concert at the end, it is clear that rather than being plugged in to amplifiers, Zack and Lisa's guitars are actually connected to their outfits, meaning it would be impossible to achieve the ideal sound required for a concert.
When the group's record becomes a hit, the title of the newspaper article reads "Did We Ever Have Chance" rather than "Did We Ever Have a Chance".
As in the episode Jessie's Song (1990), here Kelly is a great singer, despite it being noted that she is tone deaf in Miss Bayside (1990) and other episodes.
Back in The Last Dance (1991), Jessie was was in the band. Not sure if she was just covering for Kelly (it didn't seem like that was the case) but it's never mentioned where Jessie was as far as not being in the band for this monumentally big episode.