I've had several situations where other aircraft flew distinctly non-standard circuits (or parts thereof) for reasons that were very much valid to themselves at the time. The conversations afterwards were always useful to both parties and while I can't say that I've significantly improved safety across the whole of GA, I think that every little bit helps. Just accepting that we can't see everything is not a step towards a solution or an improvement in my view. A better understanding can still be created, if not industry-wide, then perhaps by educating pilots, one confused soul at a time... (tongue firmly in cheek there).