0630 should be the sleeper closest to the dining car. With the sleepers (and I think the rest of the train but I'm not 100% sure) multiple cars of the same type are numbered going away from the dining car. I'm sure there are exceptions on some routes, though. But I do not know of any offhand.
No. 630 is the last car, farthest from the Diner among the regular sleepers. I can say with some certainty because I was on car 630 a few weeks back and I was in Roomette 9 (eventually, read on
), and made good use of the railfan window. 631 is closest to the Diner. behind that is 632, and behind that is 630. Don't ask me why. It is just the way it is. I am also certain that it was not a once off thing that day, because I saw the 30 car in that position in the consist on at least 4 train 5 and 6 that we traveled on during the OTOL Fest.
I was originally booked in Roomette 10 on 631 DEN - CHI. but unfortunately the lady who occupied that room coming into Denver barfed all over the room rendering it unusable. So I was sent off as a refugee to car 630 and got Roomette 10. But within an hour of leaving Denver the door of my roomette fell off its track! So I was moved to Roomette 9 which happened to be vacant too. And the train went with two roomettes bad ordered.