Traveling Amsterdam-Brussels with KLM ticket on Thalys: When / where does my ticket get stamped? [duplicate]

Just back from my trip to Amsterdam / Brussels and I can share my experience.

1. My Thalys ticket was not checked until the train had left Rotterdam. As a result, the earliest opportunity I had to disembark was Antwerp. Doubling back to Amsterdam from Antwerp took substantially more time, and was much more expensive. However, YMMV. It was not clear whether this was true for all cars; could be that people further back on the train were checked before Rotterdam, or it's possible that conductors wait until after Rotterdam to begin checking tickets.

2. The conductor scans your ticket with a 3D barcode reader. He also has a physical stamp that punches a small hole and time/date-stamps the ticket, which is what KLM says you need, but the conductor did not use it until I specifically asked for the physical stamp. This was surprising to me, since KLM makes such a big deal of it, and there must be many people riding the Amsterdam-Brussels train with a KLM ticket.

3. For the return trip to Brussels, check-in was at the KLM-Air France desk at Brussels-Midi train station. (This is where they issue your boarding pass for both the train and plane segments home.) Despite KLM's insistence that I would need to present a stamped ticket from the Amsterdam-Brussels segment, they never asked to see it. It was not clear to me whether this was because their system ties into the Thalys database and saw that my ticket had been scanned electronically, or because they do not enforce the 'stamped ticket' policy as rigorously as claimed.