In the book it's indicated anyone holding a arriving campanha ticket can extend to Sao Bento. The converse is not addressed. Can I presume my camphana departure would get me from Sao Bento? How they'd have time to check I have no idea but I figure the price of a ticket would be miniscule compared to getting hit with a fine
I'm confident that you can assume the same ticket pricing and features in both directions.
CP website says: "Passengers who buy tickets to or from Oporto-Campanhã, Coimbra-B and Lisbon Oriente, can use the respective urban trains free of charge to get to Oporto São Bento, Coimbra Cidade, Lisbon Santa Apolónia, Areeiro, Entrecampos and Sete Rios."
Thanks, it worked and as I suspected no check in any event.