Correct. The 19128 is the full vista dome car #507 from 1992. The 19138 is the duplex roomette car "Indian Lake" from 1995. There was a second B unit 8103 (6-18103) that was released as a stocking stuffer (1991?). Rumor back then was that it was shorted - like 25% relative to the number of ABA sets sold. Demand and prices skyrocketed and it went for $500 in the back of CTT back in the day.... People complained, and Lionel released a third B unit with no number, and it was marked "water" as 6-18115.
I had just graduated college, had my first job, and saw this set at my LHS "Train Depot", but it was missing the stocking stuffer B-unit. I searched through CTT and found that the Choo-Choo Barn in Strasburg had it in stock, with the extra B-unit, at list. I asked if they would hold it, then drove from DC and purchased my first train ever. Still have it today.
And I laugh to myself when I see this set up for auction at some ridiculously low price relative to what I paid. And have seen that $500 B-unit for $75 at York many times.... 
