I'm brand new to the group and the C&NW is my area of interest.
In reference to "400" and the North-Western, it began with passenger service between Chicago and Minneapolis/St. Paul in 1935. It referred to 400 miles in 400 minutes and was in direct competition (speed) with the Milwaukee Road.
As time passed, the "400" moniker became well known and was applied to other passenger routes as well. It became so tied to the C&NW that the logo began to be used on freight service as an easy identifier.
A quick search for the history of the C&NW will provide details about the timeline info.
