Index/Match from 2 sources of files

Hi Everyone,

I have a problem with Index/Match formula looking up from two sources file. I have a summary file with the list of PO#. The objective is to look for the CBS from two files (2010 & 2011). Sometimes one (1) PO# is having two or more CBS from the two files (2010 & 2011). I need to have a formula that will indicate all CBS that are under that PO#. If no CBS, just return value as "None".

I attached the file and also put the source two sheets (2010 & 2011) in the same file for easy reference. Although this 2010 & 2011 sheets will be a different files.

A friend suggested REPT but in the end we couldn't figure out how to use that.

Thanks for your help.
Ricky