What's happened for a very long time is third party manuals. My Grandmother's copy of "Book of The Ford" was a guide to repairing the Model T and was not written by the Ford Motor Company. That was in the early 1920s and was nowhere near the first edition.
Back then, it was reasonable to make repairs to a vehicle with nothing but basic mechanical knowledge. Today, it isn't. You need torque specs (which aren't just based on bolt sizes no matter how much people want that to be true) and the codes to instruct the computers as to what to do. Those codes are in the official documentation most of the time, for recoding the PCM and such. The only way they get into the Haynes or Chilton's (etc.) is if someone gets them out of the official book. Those codes are facts, and you can't copyright a fact, so it's legal to do so in just the same way that it's legal to OCR the phone book, re-layout the numbers, and print your own. But if the manufacturer weren't forced to publish them then we would be at the mercy of dealers for that information. If the manufacturer then stopped giving them to the dealers, and ran all that information through the software, then getting it would depend on a friendly dealer willing to let someone hook up a protocol sniffer, while actually performing the procedure.
It is not enough to "allow" a third party to create a repair manual.