The bands are for the number of unique records that you will process during the license period so for example if you have a database of 49,950 records, you would select the 50,000 tier. You then can process these 49,950 records as frequently as you wish during the license period.
If you were to process the full file each day you would process a total of 18.231m records (49,950 x 365) but you would only be charged for the 49,950 records. You pay a single fixed price for unlimited processing based on the volume of customer records you have within your database (or those you need to maintain the accuracy of), and not the number of records we process, improve, update or flag.