Beware that P6 can without warning change original duration values:
From:
“Much Ado about Dates” Understanding P6 Date Information
Ron Winter, PSP and F. Burak Evrenosoglu, CCE PSP
Presented at the AACEi Annual Conference
July 1, 2009
If you change the planned start date manually start date will change but early start will not change. Schedule CPM calculation will overwrite the user input with the calculated early start date. There is no warning to the user that their input will be overwritten.
The user can input a planned finish to overwrite the calculated planned finish. This change will also automatically change the original duration of the activity and there is no warning to the user.
Therefore un-statusing might be unreliable. Always the best way is to keep a copy of the original un-statused file. Unfortunately it is not always under our control and sometimes we must work with whatever files we are supplied.
Also it might be possible that other un-wanted values are left if you do not delete them, actual costs/expenses might be one of the values you shall also clear. I am not sure it is still a BUG but as I recall in older versions of P6 you could not un-mark a started an activity if it have actual resource units but it would allow you to un-mark it with actual expenses.
I would advise that when you finish your baseline create a user defined field to record the approved baseline original durations and keep it in this ways always available without need to compare with other files.
I believe a global change can go as far as clearing all actual values including activities with 0 original duration/milestones with actual expenses/costs but will not always be able to recover initial original duration.