I understand that because something exists on Youtube it doesn’t automatically become part of the public domain. When I said “public domain” I was referring to how IP rights can be forfeited if the product is already widely available to the public before you, the Marketplace Author, decide to get some sort of IP protection for it.
For example, you may have issues patenting a product after you have already exhibited it in a trade show (I also understand that we aren’t discussing patents, but it’s the only example I can think of without cracking a textbook; It has been a long time since I took IP law).
Basically, my point was that if a person follows a freely available tutorial online to build some blueprints, puts his name on those blueprints, and sells it on the Marketplace, then it’s going to be very hard to decipher who is actually infringing and who innocently (and legally) followed a tutorial… which could quite possibly lead to a lot of unnecessary legal troubles.
Further, if the blueprints are already widely and freely available to the public before the content was published on the Marketplace, then it’s probably safe to say that the developer never had the rights to sell it on the Marketplace to begin with.