Chris,
A few photos of mine for example. These tunics have been around and in collection since the early 70's, and were bought originally from the families; so I doubt they have been tampered with in any way. Each displays a different sewing style to every part of the uniform. It seems, troops would sew their insignia on in several stages, rank, OS stripes, SSI/discharge. So possibly, you can have three to four different thread types on one tunic.
The first set is PVT Frank Kudingo, 2nd Wisconsin then 107th Sanitary Train, 32nd Division