At the moment, it is possible to retrieve the customer's usage for the current billing period (from the beginning of the period to the day of the request) but not for past periods.

Goal: as a user, I want to keep track of my customers' current usage and retrieve this information on a regular basis for analytics purposes.

Use case #1: I retrieve usage data on a daily basis. At some point, I need to send an event with a timestamp in the past (e.g. three days back) for one of my customers, so I need to be able to retrieve the customer's updated usage for the last three days.

Use case #2: During the grace period, I send an event which belongs to the billing period that has just ended. After that, I want to be able to retrieve the customer's updated usage for the past period.