Hi Lila,
Have you explored using a Journal Entry report? As long as you have planned complete date as a tracked field in your update feeds, this will record a journal entry in the system every time the date is changed. You should then be able to report on those entries, and the report could be configured to show what dates were changed; from, to, who made the change, how many times it was changed etc.
There's lots of info about Journal entry reports in this article on WF One.
Best Regards,
Rich.