Johnny F@rt Pants
Seat pitch is measured between two points on the seat, it is officially not measured between the seat attachment points.
That is why seat cushions are sculptured inward at the base of the seat back, it is not for comfort, but to meet regulations.
Once the seat attachment distance has been determined to meet that requirement, that is used for the configuration drawing (LOPA) which the engineers use for installing the seats.
So if a row of seats is added, as is in this case, the seat pitch will reduce in the removed area to match the rest of the aircraft.
You are correct in that you will get the seat pitch that you have booked.