The really exciting part is learning that all bookings for the remainder of your trip after the no-show segment have been canceled. No joke.

This is not really supposed to happen, and it can be a real pain when it does. Most GDSes have a keyword that can be inserted into the PNR to prevent autocancellation.

Yeah, I had a bad experience because of BA chekcin agent at CDG.
(I described this before in this forum)
my DONEWC3:
CDG-xLHR-DXB-xLHR-xJNB-VFA-..

I arrived at CDG earlier, so I asked earlier flight for CDG-LHR.
An agnet did. HOWEVER, the system treated as no-show for the original flight.
So, after a few days, an agent at DXB said I didn't have a reservation of DXB-LHR.
Magically, only BA flights were canceled.
Subsequent CX and JL flights (JNB-HKG-CMB-SIN-HND) were intact.

BA policy, alas. Most BA fares do not allow no showing so this is an easy way to open cancelled space quickly.

You can ask them to add "prot" or protection to the PNR to prevent this.

Out of curiosity: Did you check any bags on that jaunt? If so, was the CX agent in HKG able to check them all the way to HEL? I've had two conjoined baggage-tags before, but never three...

No - I was on cabin bag only (the wonderful Red Oxx Air Boss, on which I can survive for a couple of weeks if pushed!)

Fair point - and I imagine you are right. This said, if one did have a bag to check, might it have been possible to omit the DFW-ANC-DFW and LHR-CAI-LHR sectors from the bag tags, thus checking the hypothetical bag "only": HKG-xJFK-xYVR-xDFW-xORD-xLAX-xLHR-HEL.

Nope, you can't. The computer will refuse to accept the bags when connecting through the same station. Tried LHR-xDXB-xLHR-ICN last year. Computer said no, nothing the agents tried could override it. had to put bags in storage.

Correct. There's a practical reason. When sorting bags for connection, the bag handlers (regardless of whether human or automated) won't know which pass through the airport you're on, so won't be able to figure out where the bag goes next. Thus each airport can only appear on the bag tag once.

A few years ago, I was checking in at SIN for a flight to GMP via HND.
The agent first tagged the bag for ICN. When I pointed out that was wrong, that I was going to the other airport in Seoul, they generated a tag with SEL - the Seoul city code.
I wonder where the bag would have ended up if that hadn't been noticed.

Don't the baggage tags have dates as well as flight numbers and airports encoded?

Interesting point. But one can rarely checkin more than 24 hours in advance of a flight, right?

If it's a connecting flight then the flight coupon for the second flight may be available at the time of the first flight.

In any respect the baggage system is separate from the check in system. You can have your bag tagged through to somewhere without being checked in. Although it is wise to then bring the bag receipt to the attention of the next airline.

Very common if flying between say Europe and Australia/NZ for the final flight(s) to be departing more than 24 hours after checking in for the first flight.

If using a surface segment, which city is considered the point of stopover: the city of arrival or departure? Makes a difference in terms of being able to depart from one of those cities a second time.

The following assume SYD to LAX, then surface, then SFO onwards. So, is LAX or SFO considered the stopover city when that surface segment is employed?

For example, if LA is considered the stopover city, then one could/should be able to do:
SYD-LAX-surface-SFO-JFK-SFO-LHR-...

If SF is considered the stopover city, then one could/should be able to do:
SYD-LAX-surface-SFO-JFK-LAX-LHR-...