I would add a reference column to the Posts class, which may contain a link to another post. When user B re-splits the message, you create a new entry in the Posts class that contains a link to the original message, but is listed as a message from B.
Now, when you receive messages that A is subscribed to, you will receive "repost" - you need to follow the link to get the original content from C. If you allow repeated messages about repeated posts, you may need to repeat this de-link until get to the original message.
Paulw11 Jul 07 '14 at 5:25 2014-07-07 05:25
source share