OK, so it I have a copy of the Roman Missal in front of me while cantoring I’ll have the words but unless it’s the chant version in the book, I won’t have the music. In my entire life, I’ve never had a copy of the missal in front of me. I’m not the priest. He has one, he needs it. I do not.
I agree that the correct words should be used. But to assume that everyone has a copy of the Roman Missal (usually a red book, the one the priest uses) is absurd. Whatever books the congregation has for their use almost certainly won’t be printed in 2 colors of ink.
So no, they DON’T NEED TO GET a missal in front of them at all!