There are many instances and they take many forms. It's a subject too big to do full justice here so I'll give a few instances/headings to start things off. -

There are many instances and they take many forms. It's a subject too big to do full justice here so I'll give a few instances/headings to start things off. - Treaties between nations that either extended copyright law or force the nation with the most liberal copyright laws into doing a back flip over copyright liberalization. - Changing copyright law as in the US where stuff in the public domain went back into copyright (complicated, read Wiki, etc.) This was the result of corporate lobbying. - The recent scouring of stuff that was effectively in the public domain and clearly reclassifing it into a copyrighted domain. For example manufacturer service manuals that were once made readily available were withdrawn, or restricted to authoritized service personnel only, or were reissued after being heavily redacted. This is part of the Right to Repair argument in that an unstated right to repair had always been in existence but when manufacturers withdrew once freely available information about products we now have to fight for a new right that not long ago no one would ever have thought as a right. - Copyright owners lobbying government to tighten/change the law on ophan works - those ones where there's no known copyright owner so they would have less competition. If I recall about 70% of all works fall into this category. BTW, there's a lot more to this than I'm mentioning here. - Iteas and stuff that's been common practice and thus not documented gatherered up and put into the private (now-copyrighted) domain by unscrupulous carpetbaggers. - Programmers using public domain information, modifying it in trivial ways then claiming copyright over it. Obfuscation through copmliation makes it difficult to unravel these tricks. There's much more, here's a link I've just found that adds a few more: https://blog.kitware.com/stealing-from-the-public-domain/ https://blog.kitware.com/stealing-from-the-public-domain/