--- skip
>As long as multiple transactions do not affect the same set of rows, the appropriate triggers will fire as part of the transaction.
>
>-Mike

Hello, Mike.
I guess it sinks in on me. If we have two transactions (T1, T2). T1 starts first, fires the trigger, but does not finish when T2 starts and also fires the same trigger, then it is possible that @nNext value will be the same in both triggers.

My initial approach was narrow-minded, i assumed that the trigger will only fire within the framework of a separate, single INSERT.
Best wishes.
Kamil.