I believe that the interpretation of "Yesterday" in this article is wrong. The film is based on the Mandela effect, in which one or more people inexplicably jump to another alternate reality where things are different or do not exist. Throughout the film, Jack discovers a series of differences in this new reality: the Beatles and Oasis never existed, Coca Cola was never invented, Harry Potter was never written, etc. These things have not been forgotten; they never existed in this world. In the alternate ending, Harry Potter exists in this reality, but he did not exist in Jack's original reality, which would make for a much more interesting ending.