Our Centos Are Not Themselves Authentic?

If the parts of a work are not themselves authentic, but the whole is, what does that mean for one's definition of authentic? Our Centos are essentially taking other peoples’ idea and smashing them together to create our own chimera. poem. This could also be said of Guernica because Picasso was not in Guernica when it was bombed. If the Centos are not themselves authentic how can Guernica be? The feelings are real in Guernica, but are not (arguably) in our centos. Does this distinction give more weight to one than the other? The Centos were written with sentences borrowed from other people throughout the ages. We didn’t put thought into the meaning before we started creating them, although one could say that they had significant meaning when they were finished.
The same idea applies to Guernica. The painting is made of scenes of war, not all all part of a bombing. The scenes are not original themselves, but Picasso puts his feelings about the Bombing of Guernica into them. He had clear intent from the beginning and a rather fluid meaning at the end. Another example is the song You’re Missing by Bruce Springsteen. Springsteen wrote the song about 9/11, but he himself was not there. Does this lack of personal contact mean that his song is not authentic, although the lyrics and the meaning are original and his? His song is authentic, by our standards, at the end and by most of our standards at the start too. So is it really at the end of the process of creating the works that makes them authentic? Or can a work be authentic from the start without personal contact to the event they are creating the work