Each data provider has their own calculation models in use. Although they all use similar parameters in their models (score cards) like balance sheet ratios, payment experience etc, they may vary from agency to agency, as well as the weighting of each parameter. Therefore the results can be different.
Also, collection, aggregation, verification and editing of data happen slightly different in each agency. However, each of them has its own quality management process implemented, to ensure high quality standards, dealing with questions about how accurate, complete, timely and consistent data is.