Lets stick to O gauge on this one. What company, year and set came out with the greatest number of cars included in the set? If steam lets not include the tender, but do include the caboose.
The one I know of is…
Lionels 75th anniversary set. 6-1585.
It came with a U36B, 3 boxcars, 3 reefers, 1 hopper, and 1 caboose.
8 cars plus an engine
All the other sets were either 6 cars or they were for seperate sale. I don’t know alot about the postwar era, so there might be something else.
I know that some of the Marx sets from the 1940’s had a large number of cars. Some of the military sets had lots of cars. I also know that Marx made sets with two trains in them.