If I understand correctly what you are trying to accomplish, I think you can find the answer in my recent blog post "How to use As-of-date" table:
or in a very detailed article by Gysbert Wassenaar:
Both articles explain techniques on using Flags to work with previous time periods. In your case, you might need to get even more creative, to enable the range to be selected by users. However, the technique and the line of thought could be useful in your case.