Sorry, just to clarify the train question.
We have tickets for, say, the IC XYZ train that leaves Milano at 1200 and arrives in La Spezia at 1500. IC XYZ stops in Pavia at 1230 and Montereggiano at 1430. I take it that since Pavia and Montereggiano are stops between the ticketed points (Milano - La Spezia) we can get on and off that one specific train anywhere en route between the ticketed points? No intending to use the ticket the day before or the day after. Just on the day for that specific train.