yes-evident-in such a case youll have to stand. Mostly untill next stop (maybe 15 or 20 mins onward)-where there will again be pax leaving+boarding. In such cases most often seats are labelled on screens if/where they have been REServed. THis is very, very common and youll not be the only 1. Trains are not planes-no checkin, no boarding pass, no etc.

Very much same same as any US metro/subway or the NewJersey commuter or Caltrain or so.

OK.  Thanks.  I wanted to make sure that I wouldn't be fined or told to get off the train.  Standing is not a problem.

No you will not get a fine, but if the train is too full (mostly in Germany and Austria happens this quit often currently), they will say (on long distance trains) that people without reservations have to leave the train and get a voucher about 20€ for your next Ticket purchase. 

OK.  So the train company will give The Ticket Holder a credit voucher for about 20 Euros if the train is too full and we need to get off the train?  

Thanks to all of you out there.  You all have answered my questions and made the process of train travel in Europe more transparent.  It's helpful to know what options are out there. 

Mark & Dana Carter