I don't know why this question was ignored when it was posted 10 months ago.

As I understand it, an author/composer doesn't lose his rights to a song (book, picture, or any other copyrighted material) because of what other people do with his work without his permission. He can only lose it by his own actions, for example, if he publishes it without a copyright notice.

If you use someone else's copyrighted material, say, in the mistaken belief that it is in the public domain, you owe royalties to the copyright owner. It doesn't matter that you might have heard it from some third party who failed to correctly attribute it.

If it seems unfair to you that you might get stuck paying royalties that you hadn't planned on, consider this: It would be much more unfair if the author lost the ability to collect royalties through no fault of his own.