One example discloses a system comprising a computer comprising a memory to store machine readable instructions. The system can also comprise a processing unit to execute the machine readable instructions, the machine readable instructions comprising a data collector. The data collector can receive a plurality of verification records from a printer. Each verification record can characterize a usage of a given replaceable supply at the printer. The data collector can also evaluate a verification history of the printer based on the plurality of verification records to determine a usage credit for the printer. The usage credit can correspond to a number of authentic replaceable supplies consumed at the printer.