This paper looks at a case study in the commercial procurement of an IT system to support learners on short educational courses. It compares the use case model created before the system was built with the use case model after the system was delivered. The original use case model was created through the application of a requirements pattern language designed to be employed during the procurement phase of an IT system. The final use case model was reverse engineered from the working application. The objective was to discover how accurately the original model represented the final application to provide a measure of the potential usefulness of the pattern language during procurement.