Current Portfolio on Past Fact

Hello,

We want to be able to see the our Sales Fact Table with the SalesPerson Portfolio at a specific point in time (often current one)

This approach can be usefull:
- to be able to set objectives of the Sales Person based on their current client portfolio.
- to assess how sales person were able to make their portfolio evolve over different period

We have the
Sales Fact Table:
Client / SalesPerson / Date / Gross

SalesPerson Client Attribution table:
SalesPerson / Client / From / To

What we want is to have be able to do for instance a report as follow:
SalesPerson / Client / Year / Gross / Gross Reaff (with portfolio 01/2001) / Gross Reaff (with portfolio 01/2002)

The Gross Reaff must show the Gross with the portfolio of the sales at a specific point in time.

We are working on SQL Server Analysis Services, so we can define MDX calculations

But we are wondering the best way to modelize this

Thank you