I think that those of us who post public domain folk songs on You Tube are in a unique position, because since so many of these old tunes will have an arrangement which is protected by a copyright, it seems inevitable that we will be flagged sooner or later, even if we are using our own original arrangements. It seems that the thing to do is to first of all make sure that what we are posting is in the public domain in the first place, and then to challenge each challenge as it comes up.

Evidently You Tube derives one third of its sizeable income from this "content ID" system, and there does not seem to be a whole lot of incentive to make the system more efficient.