We need to keep a log of all post edits and reports/report actions.
So every time a post is edited, the editor has to enter a reason for the edit, and the changes are recorded along with the timestamp and editing person.
In addition, events related to reporting the posts to the moderators are also recorded.
So who reported it, when and why. Who picked up the post report, and their comments. Who closed it off etc.
The log of all this activity can be used by the moderators to see the full history of a post.
User permissions will need to apply to what user groups can see the log. The permissions should be separately definable on a usergroup basis for the ability to view the portion of the log relating to edits, and reports. You would usually want users to be able to see the edits to their posts, but not the reports.
When viewing the log, it will be possible to compare two versions of the posts.
This post editing system is live as part of our forum AVForums. However, I think adding the post report log to it will give a more complete history of the life of the post.