(Excel 2010) can anyone help me with this problem?

(I took the screenshots in Google Docs because I don't have Excel at home, but at work we have Excel 2010)

This is the folder I want to create (with sample data):

And I want to refer to this separate folder:

I want to display the item expenditures of the last 6 months (not beyond) of each individual item in "item expenditure last 6 months" in the "stocktaking" folder.
For this, I would like to refer to the "Expenditure & stocktaking" table in the "Item Databank" folder – specifically from D4 and onwards.

Both folders are saved in "M:\Warehouse Management" under their respective names.

The date in "stocktaking" automatically remains current.

Which formula do I need to insert into C5 of "stocktaking"?
If it's not too much trouble, I would appreciate an explanation.
Thank you in advance!

(Images are in English because I also asked on an international forum – but it is the German version of Excel 2010)