Ok is the issue we are all discussing sample clearance? Or copyright violation. Two distinctly different issues.
Here is an article on Sample clearance. How much exposure is your use of the sample getting? When are you at risk. When performing samples at a club "a live situation" the Owner of the club is at risk not the performer. But, I think we all already knew that.
http://www.nolo.com/legal-encyclopedia/permission-sampled-music-sample-clearance-30165.htmlOn the topic of copyright infringement I don't think 12 bar blues are exempt from protection. Even though they have the same chord pattern, slip in a solo, melody, or hook, noticeably similar to "Said Artist" and "Said Artist" has a right to claim you have stolen his musical property.