Working with large and very large data sets, you may find that an error will creep into your calculations. To avoid the tedious scanning of thousands of records for verification before sending a report or analysis to your supervisor, I will describe to you how you can avoid it. Do you know array formulas?
For some unspecified reason, the data.difference function is not automatically suggested. Especially for you, I present how to use it :-). Since it is a "ghost" function you will not find it anywhere - neither on the function list nor in the Excel documentation, and you have to enter it completely yourself.