On Facebook, if I create a post with a custom list of friends, and then later add more friends to the custom list, does that post show as a new post from me on the newly added friends timeline (even though I posted it say a few days ago), or would they only see it by looking back on the day it was originally posted?
Let’s say John is one of the friends you tag after the fact on a post that you made on December 25, 2013. At the time you tag John in your post, John (and eligible friends) will see at the top of his newsfeed that he was “tagged in Nick’s post from December 25, 2013.”
However, since the post is yours, you’re the one that decides the date that it appears under in the timeline. In this case, it will appear in John’s timeline on December 25, 2013, same as you.
If you ever change the date, the post will move in John’s timeline as well. That’s because, once again, the post is yours. What appears in John’s timeline is merely a reference to the post that you made on your own timeline.