One way to do this is to determine a data point on each row that is
common to both spreadsheets. It may be a customer name, account
number, something like that. Then use a COUNTIF formula that counts
the occurences of that data point on the other spreadsheet. Any zeroes
that result from the COUNTIF are missing on the other spreadsheet.

Impress your boss: perform this operation on *both* sheets to make sure
you have captured all the data.