I just want to throw my experience in the mix as for advertising jobs that are already filled. Twice in my career, years apart, I was consulting at businesses where I was offered a full time position but the company needed to go through the process of advertising the job and taking interviews with other applicants before I could be hired. I don't know if it was a legal obligation or just common company policy but it's a real thing.
I was told both times that it was a formality and the job was already mine. I just had to go through the motions of turning in my resume and going through interviews and -- SURPRISE -- I was offered the full time position both times. It's really unfortunate for people that get their hopes up for a job that was never available but it's a common practice.