what is the best way of schedule UPDATE

HI,

WHAT IS THE BEST WAY TO UPDATE..IS TO RUN THE SCHEDULE AT THE NEW DATA DATE ,THEN ENTERING THE NEW DATES AND PROGRESS IN THE SCHEDULE..

OR

TO KEEP THE OLD D.D ,THEN UPDATE THE SCHEDULE THEN RUN THE SCHEDULE AT THE NEW D.D

WHAT IS THE DIFFERENCE AND WHAT IS THE BENFIT OF BOTH WAYS.
OR WHAT INFORMATION WILL HELP IN BOTH CASES.

THANKS

ALI
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