Depends what you are talking about.
Micro engineering makes code 70 flex track and switches and code 55 flex track. If you use code 70 you could use all commercial components. Code 55 flex could be used on siding and yard tracks.
Having said that, I do handlay all my track in code 70 and code 55, just because I can, it allows me more flexibility in the design and its cheaper.
I model 1900-1905 and do NOT model the "old west". If you draw two lines, one E-W and one N-S that cross through St Louis, in the 1880's, 1890's probably 75% of the US rail mileage and car fleet will be in the eastern half and 50% of all the US mileage will be in the NE quadrant. By 1910 there wasn't a point in Iowa that was more then 10 miles from a rail line. Some western states, Utah and Nevada for example that only had a handful of lines that crossed the state. The PRR had a couple classes of hopper bottom gon (coal car) and boxcar that those classes alone had more cars most western railroads had cars of all classes of all types.