TOPIC: Double tapped 15 and 20 amp breakers-

I think there is a difference in these types of situations.  When I call out a double tap, it is because there are two conductors installed where only a single conductor is allowed.  I would not consider a breaker designed for two conductors to be double tapped as it is meeting the design specs.

Mike K, it's a double tap. Call it out and move on. No over analysis needed.

What types of breakers will allow two wires or is it easier to ask which ones don't? 

As far as I know, Square D has those type, but not all Sq D are designed for it. The square washer under the screw is designed for two wire connections. What makes double-tapping a hazard is that the screw and washer can't make good contact on both wires, whereas the Square D type is made for it. There is still the issue of nuisance tripping due to excessive amperage, which I would mention in my report.

Michael,
I've seen the square D breakers with the washer I think you are referring to.  Those are the type that have a notch on each side?
Have a good night    

yes sir, that be the ones. see ya next time, Mike!