Are the number of unique passengers per airport counted?
Short answer is no, mostly they are not counted. Even if they have this data it is very unlikely that they publish it.

Assuming that you are not a transfer/transit passenger; meaning you have arrived to airport by ground transportation for your departure and you have left the airport via ground transportation when you have arrived; you will be counted as 42 times in the statistics (21 departure + 21 arrival). This is standard counting method.

If you arrive to the airport by a plane, you stay inside the plane and you leave the airport with the same plane; then you are a transit passenger which is counted 1 time.
(You are not a departure or arrival passenger, you are a transit passenger)

If you arrive to the airport by a plane, you leave the plane and you leave the airport with the another plane; then you are a transfer passenger which is counted 1 time.
(You are not a departure or arrival passenger, you are a transfer passenger in this case)

So passengers of an airport are basically; departure + arrival + transit + transfer
(Note: Exact definitions of transit and transfer might change from airport to airport)

Most of the time, especially in smaller airports, airport management does not record passengers on a unique person basis. They simply don't have the unique identifier for each passenger, such as a passport ID number. So they cannot know if a person is travelling first time or fifth time.

However, there are exceptions of course:


There are (very expensive) software that allows airport management to record, filter, manage each passenger data with extreme detail. Its work logic is that it records a special text message that airplane sends to airport before arrival.
For "international" departing/arriving/transfer passengers, this unique traveler information can be obtained from the system of the passport police since they record ID numbers of passports.
Airlines might have this data separately; however this is not a feasible approach since airlines mostly do not share this info.