What you're looking for is an "accumulating snapshot" fact table. This is a fairly common data-warehousing pattern.

There's heaps of information on how to create them which I won't repeat here, but a great resource is the Kimball group who pretty much invented this (or if they didn't they certainly created a succinct definition) :

http://www.kimballgroup.com/2002/06/13/design-tip-37-modeling-a-pipeline-with-an-accumulating-snapshot/[/url]