A data transformation system receives data from one or more external source systems and stores and transforms the data for providing to reporting systems. The data transformation system maintains multiple versions of data received from an external source system. The data transformation system can combine data from different versions of data and provide to the reporting system. As a result, external source systems that do not maintain data in a format appropriate for reporting systems and/or do not maintain sufficient historical data to generate different types of reports are able to generate these reports. The data transformation system can also enhance older versions of data stored in the system or exclude portions of data from reports. The data transformation system can purge older versions of data so that older data that is less frequently requested is maintained at a lower frequency than recent data.