The question is still not clearly answered....at what point in time, or distance perhaps, is someone on a reserved seat or sleeper accommodation considered a "no show", and their reservation is canceled, allowing resale?
Is it variable by route?
For long distance trains, tickets were voided if not scanned within two hours of departing the ticketed station. That voided all subsequent segments on that reservation.
Not sure if non-NEC corridors had a shorter time limit. I am reasonably sure the NEC did.
I had my return PDX-EVR voided on the Cascades when the conductor failed to scan my ticket/check me off on the manifest when I boarded at EVR. I was the only BC passenger boarding at EVR, so they knew I was on. I think they meant to just check me off without bothering to scan, got busy and forgot.
The result was Amtrak reinstated my return, but in coach. I lost my BC seat. A disappointment, not a catastrophe.
The consequences of a missed scan on a sleeper trip with connections would be much greater. Since that incident, I have made darn sure my ticket was scanned by the conductor on sleeper trips, even if I had to chase the conductor down (which I have done). I didn't trust to the attendant informing them of my presence and their checking me off. The consequences of a missed scan, losing all subsequent sleepers, was too great to risk not ensuring a valid scan in person. I also always made sure to put returns, and any other overnight layovers, on separate reservations to put firebreaks in my trips.
There have been reports that Amtrak has stopped voiding tickets for "no-shows". I cannot confirm that and will not change my practice of ensuring a valid scan.