"What’s new?" and "What has changed?" are questions users of Knowledge Organization Systems (KOS), such as thesauri or classifications, ask when a new version is published. Much more so, when a thesaurus existing since the 1990s has been completely revised, subject area for subject area. After four intermediately published versions in as many consecutive years, STW Thesaurus for Economics has been re-launched recently in version 9.0. In total, 777 descriptors have been added; 1,052 (of about 6,000) have been deprecated and in their vast majority merged into others. More subtle changes include modified preferred labels, or merges and splits of existing concepts. We here describe how these changes were tracked, making use of the published SKOS files of the versions, loading them into named graphs of a SPARQL endpoint and executing queries on them. An ontology supporting version and delta description and query formulation is introduced. High-level visualizations of aggregated change data and drill-downs to the actual concepts are presented. We finish with an outlook to the skos-history project, which generalizes and extends the methodology to different knowledge organization systems.