I'm writing validation rule on custom object to check if created date is greater than date of releasing the validation rule to production AND( ISBLANK(Last_Purchase_Date__c), DATEVALUE(CreatedDate) >= DATEVALUE("2020-03-03") )

Hmm...Not sure if this will work, but give this a try. I think the Created Date is not established on new records yet. So if it is a new record, then use TODAY() to compare to the Date of the VR implementation. If not, use the Created Date. Let me know how this works out.

AND(
  ISBLANK(Last_Purchase_Date__c),
  IF(ISNEW(), TODAY(), DATEVALUE(CreatedDate)) >= DATE(2020, 3, 3)
)