Jazz singing is an oral tradition.
You need to listen to multiple recordings as you begin to prepare a song, for one big reason. It’s this: the interpretation of the song has evolved away from the original sheet music and into something living.
Only by listening to multiple recordings can you start to see the interpretive bulls-eye for a standard. When you’ve listened to five or ten different interpretations, it becomes clear what element is an accepted “standard” part of the song and what interpretive element belongs to a specific interpreter. You know what musical elements are on the bulls-eye and what musical elements are on the wall next to it.
If five out of five recordings make identical or similar choices, that is a standard element. You’re smart to either make the same choice or make sure your deviation is intentional. But if only one out of five recordings make a certain musical choice, you are free to take or leave it, trusting that it was the choice of a specific interpreter.