Multiple years of TurboTax can co-exist on the same computer at the same time. The problem with some of the older years installed from a CD is that they *may* no longer update. TurboTax doesn't officially support prior to 2011, so I'm not sure if those older CD's will update, or if the state program can be downloaded (if applicable). CD's come out very early in the season and have the early season forms prior to updates and finalizations. If you had download installation files for those years, however, they might be more up-to-date since the ones in your download account are updated periodically.
