Originally Posted by
Ratatoskr
I thought hidden-city means leaving the return flight a stop earlier (usually to save money).
You are correct - this is exactly what the airlines call this behaviour.
It mostly does happen in order to get a cheaper fare to the "desired" city by instead booking a flight that connects in your "desired" city onto another city; but as you have shown, the reasons that customers end up doing things like this can be for slightly different reasons rather than setting out to cheat the airline out of money.
However, when you jump out at a city that was booked only as a connection point, then you are engaging in "
hidden city ticketing".
Originally Posted by
Ratatoskr
I know nothing will be cancelled, and I have no checked-in luggage, but my concern was more that airlines disapprove of not using all the booked segments.
In general, unless you do this frequently and somehow come to the airline's attention, it shouldn't be an issue. And, as you are aware, doing this with checked-luggage is a no-no (unless your onward connection from AMS is the next day, or operated by train or bus. KLM does charge a hefty fee to have bags retrieved from the luggage system at AMS if they are checked through to your original destination, and most outstations will NOT short-check bags unless your onward journey from AMS is the next day, or by train or bus).
If it makes you feel better - don't add your FFP number to your Rome flight. You can do a retro-claim for that flight in the coming weeks/months.
Note that your AZ flight may not earn in Flying Blue (check the earning tables) so there may be no point putting your number in that booking, anyway.