According to the manual counters "CNT" are retentive on power failure, I assume this is only if a battery is fitted See P28 of this manual.
Not used Omron in many years so CNT function may be different than the "C" type, many PLC's now support internal counters as before i.e. "C001" and the IEC function "CNT xxx" so it may be that only the latter is retentive.