Originally Posted by lpjanssen

Well. I took the ZWE-AMS train coded KL212 yesterday, so let me share the experience.
New procedure indeed. I was able to get a digital boarding card for this Eurostar leg. It looks exactly like a normal flight boarding pass, but mentions the Eurostar carriage # and seat # - and mentions explicitly to hold on to your luggage.
I did not have to go to the railway station ticket counter anymore like we had to do before (I had to do that as recently as Oct 10 - not sure when they changed over). There was still with a glitch in the procedure for getting the boarding card through the KLM mobile app - but I was able to get it OK through the website.
The Train Manager was very diligent about checking the tickets for the KL passengers. He did not scan though, but put the traditional 'round stamp' on the paper ticket. So no electronic validation (the Antwerp railway station also does not have any electronic gate where you could scan).
At Schiphol luggage drop / checkin this was not really checked though - but I would not take that as a data point as I can imagine I am not raising any suspicion as a Belgian citizen with an Antwerp home address. It might be different for someone with a Dutch passport.
Would love to hear others experiences on this new process.