As I wrote in another thread, Europeans tend to have a different attitude towards public transportation than auto-centric Americans. But all ticket buyers expect to get a seat on a paid rail journey. In that sense, having no seat available for a passenger who wants to travel on this departure is, in current terminology, a "fail." I stood for hundreds of rides from Teaneck NJ to NYC, because I boarded at one of the last stops before the non-stop highway and Lincoln Tunnel portion of the trip.
Long ago, I had to stand on an Amtrak train from Washington DC to Philadelphia. That would be an "epic fail" in today's terms. Anyway, I think it is fair to use the term "sold out" for any substantial journey that is supposed to have assigned or unassigned seats and fails to provide them. Even successful welfare states fail, increasingly so today, as they run up against the same costs and taxpayer refusal to fund them as have harmed the United States.
I am not addressing public vehicles that are designed to make non-executive, non-VIP travelers stand, like "bus gates" on the airport tarmac, or Airtrain vehicles desgned to pack-em-in. But is it any wonder new pop singers get quoted, "I'll never fly scheduled again ..."