Wow, do I have an update! I found this record for Michał Jan Koczoń in the New York, Abstracts of World War I Military Service, 1917-1919 collection on Ancestry.com
According to this record, Michał was drafted and scheduled to discharge as Private in Company K of the 306th Infantry on Dec 6 1917. He was discharged on Mar 11 1918 – having received no wounds. On Jan 27 1918 he is marked as an ‘Alien Enemy’.
Michał came to the USA in 1912, visiting his brother Franciszek in Brooklyn. In 1915 he was living with the family of his brother Tomasz on Seventeenth Street. By 1920 he had married Wanda and moved to 22nd St, but by 1923 he was living at King’s Park in Suffolk County as an ‘inmate/patient’. This is where he is recorded living in 1925 and 1930 as well.
Michał Jan Koczoń was my 2nd great grand uncle and brother to my great grandfather Tomasz Koczoń.