Usually the database keeps a history of the statistics for one table for 31 days.
The following sql will return the number of days statistics are currently retained for.
SELECT DBMS_STATS.GET_STATS_HISTORY_RETENTION FROM dual;
The following sql will show the dates statistics were regathered for a given table.
SELECT TABLE_NAME, STATS_UPDATE_TIME
WHERE table_name LIKE 'OM_ORDER_HEADER%'
ORDER BY STATS_UPDATE_TIME DESC;
In case you want to rollback specific statistics in the past use the procedure.