I thought “Rockin’ Around the Christmas Tree” was Wayne Newton, not Brenda Lee, until not that long ago.
I used to think that both Up, Up and Away (In My Beautiful Balloon) and The Age of Aquarius/Let the Sunshine In were by the Mamas and the Papas.
Sirius can lead you astray, though. I remember listening to the FirstWave channel one day and seeing on the display that “People Are Strange” is by Echo and the Bunnymen, not The Doors as I’d always thought. With the zeal of a convert, I have been going around telling people that for a while now, and it was only today, double-checking my facts before posting in this very thread, that I discovered that it is indeed a Doors song, and E. and the B. only covered it (for the soundtrack for The Lost Boys).