FPL Netmetering

Are banked kWh's (aka "kWh's Received") only used to offset future use or are they also applied to prior months within the same calendar year?

For example, if in January you used 20 kWh's from the grid and banked 0 kWh's, but then in February your net kWh usage was -20 kWh's (meaning you generated and delivered 20 kWh's to the grid over what you used from the grid), does FPL essentially wipe out your January bill or will the overage only be useful for future months?