Manipulating a .csv file to look for two common values to create a key, then summing up values
Overall, your code is pretty clean.

Here are some points for improvement:


Use the if __name__ == '__main__' idiom if this file is to be executed directly. https://docs.python.org/2/library/main.html
Structure your code so that no code is executed before the name clause or upon import. In other words, don't have any code blocks which start at the left-hand margin. Instead, place code within a few functions which are called by a main run() function.
Use an enum or constants to represent the index values for things like nd_amount.


EDIT

ND_AMT = 14
...

nd_amt = row[ND_AMT]