Q:

Multiple vlookup using index and match

I need to make a vlookup function based on two unique IDs.  So far the Internet has told me that a combined match index will do the trick.  Unfortunately are my excels skills limiting me. 
Basically I have 3 different tabs.  In tab1 I have a col with dates and one with quantities.  These are the cols I need to lookup.  In tab2 I have dates and a supplier name, while Im in tab3 got quantity information and a supplier name. 
So I wish to match the information in tab2 and tab3 with tab1 so I can see when a supplier delivered a given quantity. 

A:

So you want to get Supplier / Date / Quantity.  I guess the original idea of the problem as you set it out is overcomplicating things.  
I would personally use the table with Supplier / Date on tab2 as the starting point and add a column with a formula to that tab to get the quantity.  This formula will refer to tab1 and will work perfectly fine with just a vlookup on the date and retrieve the quantity:
So on tab2 column C (specifically cell C2):
=VLOOKUP(A2 ; tab1!A:B ; 2 ; FALSE)

Or if you need comma as separator:
=VLOOKUP(A2 , tab1!A:B , 2 , FALSE)

