It is possible for higher-frequency periods to overlap lower-frequency periods. For example, a week can start in one month and end in the next month. In these cases, FRED frequency aggregation will include the higher-frequency value in only one of the lower-frequency periods. The value is assigned to the lower-frequency period containing the daily date for the higher-frequency period. For example, a weekly period that ends on Friday 2010-09-03 will be included in the aggregated value for September not August.