ERT will read the historic rates from the Schedule file, but it is also possible to use historic data from another ECLIPSE run (e.g if historic data do not exist in the Schedule file).

SCHEDULE
  ERT will use the historic data provided in the Schedule file.
REFCASE_SIMULATED
  ERT will use simulated values from another ECLIPSE run (a Reference case) as historic data.
REFCASE_HISTORY
  ERT will use historic data from a reference case.