Indeed, does it need to be heard by a second or third party to have been played with style?Can you say a piano sonata does not exist until the pianist interacts with the piano to play it? But he can play it in his mind just as well... Others played it on the piano before him and still others will play it after him. He himself will probably play it again - does the sonata cease to EXIST in the meantime? Perhaps it will cease to MANIFEST, but not to EXIST.
Surely a musician, writer or the creator or performer of any art can feel the satisfaction of having captured something that he knows to have style whether anyone else is available to share the experience or not? Did Constable only develop style at the age of fifty three when he was finally accepted by The Royal Society?