Diegetic Soundtrack Usage vs. Left the Background Music On

So, Theme Tune Cameo was renamed Diegetic Soundtrack Usage and broadened to mean "any in-universe background music or theme tune", but I thought that was what Left the Background Music On was.

Diegetic Soundtrack Usage seems to be about Title Theme Tunes specifically, and Left the Background Music On is when it's Played for Laughs.

also, Left the Background Music On is usually a Bait-and-Switch gag whereas diegetic soundtrack usage is upfront about it

It's not, at least not anymore. It used to be called Theme Tune Cameo, but was recently renamed and expanded.

Difference is in the setup and what kind of music is used.

• Diegetic Soundtrack Usage: You recognize the song from the soundtrack already, it plays in-universe and you go "Oh, that's neat." The song has to be actual music for the show, and it doesn't need to have an "in-universe after all" reveal. It's just in-universe.
  • Bob has an upbeat Leitmotif that appears as his ringtone.
  • Bob starts humming the show's ending song.
• Left the Background Music On: Any music (not necessarily that in the soundtrack) plays in the background at first before it is revealed to be playing from an in-universe source.
  • Bob powerwalks down the high school hallway as "Don't Stop Me Now" plays in the background. Pan to the choir room where the choir is practicing the song.
  • Bob starts writing a love letter and Taylor Swift plays in the background. We then realize that Taylor Swift is playing on his Spotify.
• Left the Background Music On's inverse is Diegetic Switch: Music is played in-universe before transitioning to background.
  • Bob powerwalks out of the choir room as they practice "Don't Stop Me Now". The choir's practice then fades into the actual song.
  • Bob puts on Taylor Swift to inspire his love letter writing and it begins as tinny phone music. As he goes to deliver the love letter we hear the actual Taylor Swift song quality playing even when he is no longer using his phone.