I wanted to see the historical burn down charts for released versions (to compare with how things are going now) but a lot of the old versions in my product just have a release date, but no start date set. In the Agile feature you can change the start date of unreleased versions (by clicking on the start date in the version list on the right). But the dates on released versions in the "Released board" are not modifiable.
How do I modify the start date of a version that has been released?