Hi Richard,
Thanks for the comments. For some background, I am enrolled in Justins Music Theory and I was also watching Stevie Ray Vaughan Tin Pan Alley (with Johnny Copeland) - YouTube and thinking about how these guys know what to play.
I took a long weekend off which affords me time to think of these things. 
I have seen CAGED in my reading in several places. I know it is in my future but I haven’t been that far in the lessons yet. Good to know it will be a part of the answer, so I will try to be patient!