Well, when ROTK was released, they had special showings in some cities. They got 35mm prints prepared of the extended versions of FOTR and TT and showed them back to back followed by ROTK. And the novel was never meant as seven books. No more than the Iliad is twenty four books. Tolkien disliked having separate titles for the volumes, he would have preferred vols 1, 2, and 3. The titles were the work of the publishers. He especially disliked RETURN OF THE KING. He thought it gave too much of the plot away and would have preferred THE WAR OF THE RING. The idea of a seventh book comes from the fact that Tolkien had originally planned a supplementary book of information on Middle Earth, but working in his usual dilatory fashion was so far behind that he was forced to scrap the idea. Irritated letters had been arriving at Allen and Unwin demanding when part three was coming out? To get it finished he simply compressed as much of the material as possible into the appendices. Paper shortages (this is coming up for ten years after the war) had nothing to do with it.