I assume many pax from KIN or PVD to BOS have multi ride or 10 trip tickets. I have never seen the Conductor deny anyone or send anyone to the cafe. And I have been on full trains.

#66 departs PVD after 7 AM and arrives BOS before 8 AM, so it is used by many commuters. In fact, there is usually an announcement just before arriving in PVD that many will be boarding and that they need all the seats available.

The train usually fills, but there are seats left over. (Not too many, but some! ^)