I wonder if two lists are creating some confusion for you in this situation? If I were attacking this problem, I would create a single list called Seats with the following columns:
Status (which can be blank, Reserved, or Unavailable)
...and other handy info like flight date, seat class, passenger name, etc.
Then, I would use a Filter to display seats that are not Reserved status on the flight, meaning they could be reserved by a customer. I could also use a Countrows on a Filter of 'blank' Status to know how many seats are left on that flight.
Or, is there more to your situation that makes it more complicated?
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