We have been evaluating Vault for a long time and are just about ready to make a large purchase (for us, anyways

). I've studied all the license costs and am now determining if and when we should purchase corresponding maintenance plans. The page describing the maintenance plan (
http://www.sourcegear.com/misc/maintenance.html), has the following statement:
May be purchased only for licenses which are already current
I am unclear on what exactly is meant by "current." How long does a license last, and exactly how much time elapses before I am unable to purchase a maintenance plan after I buy the license?
Thank you for your time.