There have been times in PHL that the conductor would check the tickets before boarding on the Keystone going to NY and deny boarding to multi-ride and pass holders. This may be because the Keystone is a shorter train and there are Regionals around the same time. The situation usually arises when a Regional has broken down or is severely delayed. Again in my experience I haven't seen this happen on the Regional (and this may be because the Keystones don't have a cafe car)