Jump blues and hepped up jazz had been around, even Texas Swing but there was no "rock and roll" in the 1940s. Close but not the magic formula. Too gentle. Too big of bands.
The words "rock and roll" had been in use. So what. It is a sexual expression.
As we get into 1951, there are some cuts that could indeed be called rock and roll.
Today's radio music, by the way, is not rock and roll (certainly no roll), and largely isn't even rock.
And rap isn't the new rock. It could be the new scat jazz, doo wop, blues, or poetry. But it ain't rock and roll.
Weegee... have you lost your mind?!?!?!
"But it ain't rock and roll."
Well, you are starting to come to your senses!