Windows defense logs go a good distance to resolving account lockouts, although extracting account lockout assistance from Windows Security Logs is not always a reliable method. Account lockout guidance can be retrieved from the PDC emulator DC as it is guilty for processing lockouts. But, the PDC emulator also processes a lot of other events for the entire domain; adding authentication mess ups and password adjustments. In large environments where there a lot of users these event logs might be accrued on the PDC emulator and a big volume of logs will collect.
Subject to the dimensions limit of the event logs, you may find that the old logs were purged and the only available logs are those from the previous couple of hours.