The file names used for the diagrams are the figure numbers, e.g. Figure_5.2-1.vsdx. Inside the visio file, the page name represents the TS version number, e.g. 18.2.0. When a new CR is submitted that changes the figure, a new page is inserted with the modified figure with the new version number of the TS. Once the CR is agreed, the figure with the earlier version can be deleted.
