The only test for me that matters whether I'm piggybacking or being piggybacked is relevance and tone. I've been blocked by those it bothers when I drop links (and by the way I often inclufe links by other writers as well). So be it. I will never understand why a writer thinks they own the comment space and it should only be about them. I saw a great reply comment once to a comment I left in a story where a writer vilified another for piggybacking: "Oh wow… I don’t know enough words to describe how I feel about this. Just unbelievable. To think she owns the comment section is so very childish. I’ll just leave it at that. Thanks for sharing this."