Red Flags in Art History: Zacharie Birtschansky or Birshansky

Annunciatory Angel, 16th Century  Detroit Institute of Arts (DIA)
Provenance: Paris, Z. Birtschansky (dealer-1939), by whom given to the DIA in 1939.
Nazi Era Provenance Internet Portal

Art Dealer Zacharie Birtschansky, NARA the Wiesbaden Central Collecting Center, Vaucher Commission Lists, July 16, 1945, FOLD3  https://www.fold3.com/image/231986121 

Who was Zacharie Birtschansky? What does finding his name in a provenance mean?

According to French documents, Zacharie Birtschansky was born on May 27, 1889 in Moscow and was an art dealer with a gallery at 88 rue Faubourg Saint Honoré in Paris. Wanted for dealing in stolen art by the French, he escaped to the United States where he was thought to have stored « art treasures ».  The OSS Art Looting Investigaton Unit mentions Birtschansky numerous times, in particular in connection to Wendland and Fischer and to his partner Mandl. The name Birtschansky and Z Birtchansky appears in numerous provenances in US museums, notably the Detroit Institute of Arts Museum (DIA), to which he sold or gifted several artworks, such as Saint George and the Dragon, Annunciatory Angel, and Mountain Landscape, the NGA (Bacchus and Ariadne;  Madame Stumpf and Her Daughter) and LACMA (KAUFFMANN, ANGELICA Half-length Portrait of the Duchess of Courland; MANDYN, JAN St. Christopher and the Christ Child)