If there was an error in a field calculation, the calculation methodology has been changed or the field has not been updated for any reasons before the project closure, the calculated field just crashed, there is no easy solution to fix it, we have to go ahead and open up projects one by one and that would distort the Project's Actual Completion date.
Talking to the Support I had no satisfactory solution to fix my problem as the list of the impacted records is giant.
We badly need this feature to make our reports reliable and to enable the report specialist to be absolutely sure that the calculations are correct.