Unorganized territories (UTs) are defined by the Census Bureau in nine MCD states where portions of counties or equivalent entities are not included in any legally established MCD or incorporated place. The Census Bureau recognizes such separate pieces of territory as one or more separate county subdivisions for census purposes. It assigns each unorganized territory a descriptive name, followed by the designation “UT” and a county subdivision FIPS and NS code. The following states have unorganized territories:
Arkansas Maine North Carolina Indiana Minnesota North Dakota Iowa New York South Dakota
In the context of Maine, a township is an MCD; the Census Bureau has designated UTs because there are unincorporated portions of counties that are not part of any township. I believe this conclusively shows that the unorganized territories you mapped should be tagged boundary=census.