Wita Stwosza altarpiece
Paul Sapieha was involved in the return of the Wita Stwosza altarpiece (also known in Germany as the Veit Stoss Altarpiece) to Kraków. This involved US Army personnel convoying into Poland, then occupied by the Soviet forces.
Agata Wolska recently published Zagrabiony Odzyskany: Historia powrotu ołtarza Wita Stwosza do Krakowa, describing the altarpiece’s return — currently available only in Polish.
His report for the US Army can be downloaded as a PDF here: sapieha-report-poland-1945
His correspondence on the surrender of Paris (1944): paul-sapieha-correspondence-on-surrender-of-paris-1944
The photographs below are visible proof that Paul Sapieha was in Poland in 1945. Agata Wolska described these as the final confirmation of his role.