That something is effectively public domain does not make it legal to use. This movie was in a thousand torrents, yet one gets still sued for uploading a kilobyte of it.
That it is hard or impossible to know if it is legal to use does not mean it is ok to do so. You need a source for the license that is able to compensate you for the damages you incur in case their license was invalid.
I'm not happy about either of these points, but that's how it is currently and just closing your eyes and hoping it will go away won't work.