This is cool, but not really how publishing works. I doubt Rowling knew when her book was going to be released when she wrote it. She probably didn’t even know when she signed her book contract. I guess it’s possible that in final edits she asked to go in and make sure the date was 1998, but considering she was a previously unpublished author I doubt her editor would’ve considered that request a worthy use of time.
They have special underpants. I am no longer shocked by things that Mormons do.