Drop Down to Access Differnt SharePoint Workbooks

[Tidr0001]

I have multiple monthly reports on a SharePoint website with sales data on the "Summary" Tab.

I am using a Data Validation drop down list to ID the months I would like to pull in.
[TABLE="width: 500"]
<tbody>[TR]
[TD][/TD]
[TD]November 2013
[/TD]
[TD]December 2013
[/TD]
[TD]January 2014
[/TD]
[/TR]
[TR]
[TD]Sales
[/TD]
[TD]XX
[/TD]
[TD]XX
[/TD]
[TD]XX
[/TD]
[/TR]
[TR]
[TD]Inventory
[/TD]
[TD]YY
[/TD]
[TD]YY
[/TD]
[TD]YY
[/TD]
[/TR]
</tbody>[/TABLE]


As I change the date in B1 or C1 or D1, I would like to pull the new data in from the corresponding sheet on SharePoint.
I have a reference sheet in the workbook that provides the URL Link for every report on SharePoint.
For Example:
[TABLE="width: 500"]
<tbody>[TR]
[TD][/TD]
[TD]URL
[/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]November 2013
[/TD]
[TD]http://test.com/dpc/IM Toolkit/Archive/ Results Nov.xlsm
[/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]December 2013
[/TD]
[TD]http://test.com/dpc/IM Toolkit/Archive/ Results Dec.xlsm
[/TD]
[TD][/TD]
[TD][/TD]
[/TR]
</tbody>[/TABLE]

Formula below works but is static:
= SUM('http://test.com/dpc/IM Toolkit/Archive/[Results Nov.xlsm]Summary'!Y$2:Y$25000)

Thinking something like:
= SUM(CONCATENATE(“'”,(Index(Ref Sheet!A1:B10,MATCH(B1,Ref Sheet!A1:A10,0),2),”Summary'!Y$2:Y$25000”)