You may be right but I think he'd have a good shot at having it taken down if he pushed the issue.
Like you, I can't say with 100% for every story. I do know this, the ones that are normally taken down are the actual uploads of his audiobooks. Most of those are completely illegal. It's no longer, just Stephen King's work, but the work of the narrator, not to mention the producers, and even if the text has become public domain, the Narration may not be. The audiobook copyright may still be protected while the text may be free.
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This is very true of Edgar Allen Poe's work. His text is free, but most audio recordings are protected. Although, in Poe's case you can use his material for profit.