Qualification: I am not a copywrite lawyer but have experience with copywrite.
I can't imagine it being an issue, how can there
be a copywrite holder for something no one has made claim to.
The intention of copywrite is to protect the producer so royalties are paid when appropriate. But how can you pay anonymous? A work must be identifiable by a time made and the person who made it essentially. This is done by registering the "work".
It's too big a subject to cover easily but here is a link to Canadian copywrite. If you are looking to produce something for distribution and or profit, copywrite lawyers aren't that expensive. They can keep you out of trouble. In Canada there are facilities available to ensure creators are protected and I am sure there would be in other areas as well.
This year the diet is definitely gonna stick!