Minor blues is from the 6. The b5 of the minor blues scale is the b3 of 1. Cmin blues is from the 6. Gb is the b3 of Eb. Secondary dominants borrow from parallel minor. Summertime is from the 6. You don’t know what love is is from the 6. Blue bossa is from the 6. I can go on…
‘Laura’ is from the 6 & perfectly displays what I call the ‘Holy Trinity of Key Changes’. You borrow from 1,4,5. It’s blues baby!
4 & 5 keys even in minor (minor251=736)
1 being the parallel keys 6,3,2.