...Also, from what I understand.. The SDP is your ticket and is valid for any trips (with some exceptions), you dont need to specify which trip you are taking..
for ex. Im planning to take the train (Zurich-Zermatt) at 13.30 on the 27/2, but If I miss that one, I can take the train departuring at 14.15 (on the same day)?
Best regards,
Carl