Patents can be challenged/revoked if they are not novel - in other words, if the practice, process, invention, etc already existed. Particularly if it is in wi

Patents can be challenged/revoked if they are not novel - in other words, if the practice, process, invention, etc already existed. Particularly if it is in widespread use it is often easier to get it revoked - hence conference papers, articles, posts, etc, about this practice can prove that CD is well known and get the patents taken care of. Generally you are not required to search for prior art before you file a patent, you just have to promise you aren't aware of any. Some people intentionally avoid looking for prior art for this reason, as the patent office is overwhelmed and often staffed people not as much of experts as they should be, and you end up with people granting patents for obviously non-novel things.