Using LEFT inside INDEX-MATCH to find values that match first 5 letters of referenced cell

I'm trying to combine a "Vendor" summary sheet and a "Customer" summary sheet. The problem is some companies are on both lists and hence there are times when there is only one entry to move to the "Combined" list, and other times when there are two entries that need to be added and then moved to the list.

This the unsuccessful formula I have so far in cell C6:

Formula:

=INDEX(U6:V47,MATCH(LEFT(B6,5),LEFT($U$6:$U$47,5),0),2)+INDEX(AN6:AO47,MATCH(LEFT(B6,5),LEFT($AN$6:$AN$47,5),0),2)

Here's a screen grab of the sheet:
Combine Data.jpg

Here's a reduced version of the file (look under "Pallets - Year" tab):