Because you do not own the copyright on any of those Beatles videos and materials, you do not have the legal right to release any of it under any Creative Commons license.  The only thing you can legally license CC0/public domain from your website is any content you create yourself.  This is why OTRS is refusing your argument: that website appears to be a collector of someone else's copyrighted works. We can't use its material unless we have permission from that copyright owner, and Apple Corps. is not likely to grant that. lute