Hi dudes, **Leo **here.
I might have gotten the dates wrong, but this is how I remember it–and can add another kindred word to OP. Anecdotal, as is, of course, my dating/memory of those.
And the words first in Black slang being used by whites is nothing special at all. “’'Sup ma niggahs?”–even a Brit suburban white thought that was cool enough to say in the (great) movie Sean the Deadfrom some years ago. Over the century, from The Jazz Age to hip hop (and gangsta talk within it, and the word itself), the cultural vectors are easily apparent.
FWIW, I can only say I remember those words from about the same time and the reason when my childhood friend started calling each other “Slick,” as in “Yo, Slick,” which we still do face-to-face or in email. It stems from when we were in high school, grad 1976-77, we saw a very funny (at least then–haven’t seen it since) movie called, I think, Kentucky Fried Movie, with–if it was that movie–barely-connected skits. (I think.)
Stuck in my head is a scene of a ghetto prostitute (the word used be before “urban,” and still sometimes now, less euphemistic and more judgemental than “urban,” but referring to the same culture–one that says homey, for example. But anyway, that was a side comment above.) She was hurrying along and setting straight a completely non-plussed fumbling middle-class white guy, name unknown to her. Not sure if she was supposed to be a tranny hooker as well, or was played in obvious drag by one of the actors.
It was funny, then at least, not the least for her radically different language and accent.
And perhaps you’re right, and it doesn’t track chronologically with “Holmes,” etc., except in my head.