Harold-
While Sanborn Maps do not have exact track configuration and placement as a primary consideration they do have some utility, especially in tightly built-up areas.
In some instances they are better than nothing…for example, a Sanborn Map of the former Suburban Engine Terminal at Riverside, Illinois is the ONLY reference I’ve been able to unearth…and from what we know of the facility, what it shows makes sense and is probably pretty close to the mark.
As you know there probably isn’t any one document you can look at and take for gospel….at least when it comes to railroads. Source documents are frought with errors and often indicate what was intended to be rather than what was built. Doing “As-Built” corrections to drawings is a dreaded, dreary task in any industry and is usually a low priority. Many outdated railroad drawings are long gone, tossed out when they were no longer relevant, so sources like Sanborn Maps, Historical County Atlases, Property Ownership Maps, etc.. can supply at least a general picture of what was. USG Maps are not going to show exact track layouts either as that was not their focus.
Charlie Vlk