I think you’ve hit on something there, Mick. A lot of players, especially guitarists, seem to have a preconceived idea that the structure of a blues song is always the straight 12 bars, using chords I, IV & V. The memorable songs tend to have variations and subtleties that make them stand-out. Born Under A Bad Sign being a good example. Far too many people, in my experience, have the ‘it’s just the blues, innit?’ mentality.