If we understand the true meaning of plagiarism, then this discussion wouldn't drag. Copying someone else's work is plagiarism. Using your work is not. Even in the world of writing,an author is free to use and share his work across platforms. We need to separate search engine weaknesses from plagiarism. Every system has its weakness. That search engines have no algorithm to identify where a published work that was first shared originated, is a weakness of search engines as a technology, and not an indication or proof or supporting argument for plagiarism.