The 3 tables have data based on your data retention settings. If you keep detailed statistics for 7 days...after database maintenance runs nightly it will copy any data over 7 days old in the Detail table to the Hourly table. Lets say you keep hourly data for 14 days. During DB maintenance, the hourly data over 14 days will be summarized to daily and so on. So your detail table will have data up to the current date of collection. The rest of the tables will have data based on your retention settings.