I've got a James M Scott living in Brookfield Township Linn County in the 1870 census. He is listed as a farmer with spouse Mary C. State of nativity is Indiana with an estimated year of birth of 1834. Two children Mary I and Edith Scott are also listed both less than 10 years old which is likely indication that marriage occured during the 1860s.

This same gentleman and family is listed in the 1880 Census in Linn County as shown below, note the additional children and the change in occupation to Tinsmith.

Name: James M. Scott
Home in 1880: Yellow Creek, Linn, Missouri
Age: 45
Estimated Birth Year: abt 1835
Birthplace: Indiana
Father's birthplace: Rhode Island
Mother's birthplace: Kentucky
Occupation: Tinsmith
Marital Status: Widower

James M. Scott 45
Mary J. Scott 13
Edith M. Scott 11
Georgia K. Scott 5
Robert H. Scott 1M

Note that Robert is 1 month old and that James M. is a widower, that would make his wife Mary C. as passing away either May or June of 1880 as the census was enumerated on June 26th for that location.

Robert H Scott (the Son) enlisted in the Army at St Catherine Linn Co Missouri in August 1909 as a farmer 5'83/4" Sandy hair dark complexioned for 3 three year enlistments being discharged Ft Logan Colorado on August 5 1918.

The 1890 Federal Census records are not available to us. I do not find James M Scott in the 1900 census records for Linn County Missouri however which likely makes his year of death between 1880 and 1900 per census records.

I can not make any of the NPS CWSS James M Scotts fit when making comparisons with the MO SOS site http://www.sos.mo.gov/archives/soldiers/

Those that you listed appear to be actually 3 individuals One from Camden Co, One from Nodaway County and a 3rd from St. Louis.

Hope this helps

John R.