MS Project has 11 Baselines wherein you can save different variables to reflect shift from planned and actual values. Variables which gets saved with each baseline are – Budget Cost, Budget Work, Cost, Work, Start, Finish, Duration, Fixed cost, Fixed Cost Accural, Baseline Deliverables Start and Baseline Deliverables Finish.
Baseline 0 is by default used for all the calculations which includes Earned Value and other Variances parameters. But we can always change the Baseline which could be used for Calculations of Earned Value. Still, most of the Project Manager prefers using Baseline 0 to store the latest vaules of baseline parameters for calculations and keep copying older baselines to Baseline 1, 2 and so on.
To Change the EV Baseline, go to File -> Options -> Advance and from drop-down select the desired baseline for calculation.
Once we have exhausted our 11 baselines, we still have option to use Interim Plan to save 10 Start and Finish Dates to store the snapshot of dates. Note – we cannot save other parameters while using Interim Plan. Also, Earned Value calculations cannot be based on Interim Plan as it is just storing 2 parameters.
So in short if you are just tracking Start/Finish Variances you have total of 21 Date fields to store these snapshots Baseline 0-11 and Interim Plan 1-10.