In a later episode (Selfless), we see a flashback to the musical episode, where two new songs are performed:
Mrs. (sung by Emma Caulfield, written by Joss Whedon, produced and arranged by Douglas Romayne, orchestrated by Wataru Hokoyama)
Mustard/Parking ticket song (sung by Marti Noxon and David Fury, written by Joss Whedon)
These songs are not included in the soundtrack to Once More, with Feeling, and unless I missed something, the Wikipedia article about Music in Buffy the Vampire Slayer and Angel doesn’t mention another release where these two songs are included.
Was there any release that included these songs? Maybe as bonus material to a series DVD or so?