I have observed that some songs are sung in lower octaves than what's written on the official sheet music,
I only recall noticing this for male singers who are bass or baritones, not tenors, not that I recall,
for example I think I looked up some sheet music for Frank Sinatra, Michael Buble and etc,
I could be wrong but sometimes their vocals are octave(s) down from what's on the sheet, if the first note on the sheet vocal section is a F4, they would sing F3, and etc
I don't recall observing this kind of transposition with tenors or female singers, like Bruno Mars or Beyonce and etc, what's on the sheet is exactly what they sing
Maybe I'm mis-hearing and completely wrong, but I was wondering if it's even a thing that sometimes the vocals won't exactly match the sheet music (octave wise), and is it common?
If you listen to this song on youtube, for the very first note that Michael sings, "birds", I could be totally wrong but I don't think that is an E4, emphasis on the 4, I don't think it's E in fourth octave, I mean I listened to it and tried on piano keys and I don't think it's E4