I’m with Sandman on this. It does help to know roughly what key you sing a certain song in, or its start note - even if you don’t play an instrument or read music. If you have a songbook or crib sheet handy (let’s not go down that avenue again, please!) you can mark it in, then next time you do the same song, just ask someone to give you the key or start note. Doesn’t matter if today you’re better on Ab or Bb if you’ve marked as A and are singing unaccompanied, but at least you’ll be in the right area.
And how many times have you seen an unaccompanied singer start a song and then stop? “Oh that was too high/low!” then start again in exactly the same key?