Most Polish POW's were captured after the capitulation of the 5th Division on 11 January 1920 at Ujar train station as well as during the Soviet offensive in the early August.
Only a few Polish POW's were captured in other engagements, as the Soviet offensive terminated with the Battle of Warsaw.
[1] While majority of Polish POWs were held by the Soviet Union, several thousand of them were held by the government of Lithuania - soldiers captured during the Polish-Lithuanian War, Żeligowski's Uprising or interned during the Polish-Soviet War (Lithuania was sympathetic to the Soviet side; see Soviet–Lithuanian Treaty for further details).
Cases of mistreatment of Polish POWs in Lithuania were frequent and similar to situation in Soviet camps.
[2] Poland and the Soviet Union exchanged prisoners after the Peace Treaty in Riga was signed in late 1920.