At the moment I am using DDL with Windchill and the broken down version on intralink. This also uses the Baseline feature. To my knowledge and what I have seen, you can set the base line at any point in the part or Assy life cycle. As you continue to work on that part or assy you can always revert back to the baseline you created. Look at it as just saving your initial save on your original part instead of purging it. You always have that to go back to create a new version or variable of that particular part or assy.