When the need for rebaselining occurs, you have a couple of options to track
Start dates at that point:
1. Save the Start, Finish, Duration, Work, and Cost information in
Baseline1-10 fields
2. Save the Start and Finish date information only in the Interim plan
fields (Start1/Finish1 - Start10/Finish10)
You would perform one of the above before rebaselining your project. Hope
this helps.