The availability of representative data samples, models and statistical information derived from the analysis of parameters that adequately describe the state of the ionosphere are key elements for the design, verification and qualification of EGNOS algorithms. As part of the on-going evolutions of EGNOS V2 releases, and also in support to the development of a future multi-constellation and dual-frequency SBAS (EGNOS V3), ESA has started a refinement process of the tools, data and precise definition of the ionospheric operational conditions. A particular driver for this process is the improvement of the availability performance of the current and future system especially under solar max and severe ionospheric conditions, without degradation of integrity and accuracy performances. The paper provides an overview about the concept and the data and models used for EGNOS development and qualification. It outlines the approaches to generate reference models and describes the parameter used for the characterization of nominal and perturbed ionospheric conditions from an SBAS perspective.