I have a master list of data and a shorter list (subset of the master) of
additional data. When I use vlookup including the FALSE argument, I get #N/A
for all data lines that don't exist in the subset list. When I use the TRUE
argument, I get incorrect results.

Both lists are sorted in the same order. The lookup value is alphanumeric.

How can I use a vlookup function and not get an #N/A result?
Once I get an #N/A result, I can't do any other mathematical functions on
that data.