Hint 1: The four theme answers are the four longest answers
Hint 2: They all have something in common that relates to 71A
Hint 3: Google "Shania Twain songs" and look for a song that shares this common property... the song is from 1997
Bonus Hint:
In @MikeyG's "Pun of a Kind" Puzzle #66 titled "Head Out on the Road" (also published today), his entry "SORRY I"M OUT" would make a lovely sixth theme entry which was clued "Yeah, yours truly is no longer attending your calculus party, Mikey..."