Today's update included a number of additional features. One of which is Concept Versioning.
Now when you replace a concept you will see the option "Version Concept". If you select this option, the old concept will be versioned for future reference only. Once versioned. The concept options will now include "Older versions", which contain a dropdown list of the older versions. You can click a version to view it with the latest concept side-by-side. You can also view other concepts and comments in the same dialog.
Please let us know if you have any feedback on this new feature.