how will Index Match work with name range over 12 sheets or with a VBA.

I am not understating how a name range (name range has 12 sheets named as 12 months)works with index match over several sheets to take data against specific cell. I am doing this with a very long formula that is also hard to understand even after several tries. So 1st i need a short formula or no problem if someone can tell me how to do it with a VBA in sheet "Style Details".
2nd i want a double checkup formula in sheet "Credit Note" in QTY column cell E13. which should work like that if i put an invoice# in cell A13, cell E13 1st take it's style no. from sheet "Style Details" and then take that specific Style No. QTY from anywhere in 12 sheets.
My Data in 12 sheets are in same cells. Sorry for poor English if i couldn't explain properly.
test.xlsx

Thanks