Where do fake art provenances come from?

WARNING: Art historians who cite these sources should know that they contain omissions and outright lies concerning Nazi looted art.

"The painting was bought at the auction in 1940 by a Dutch man, S.B.S. Slijper"

see: Heirs Sue for Return of a Kandinsky, Saying It Was Looted by Nazis, NYT,  https://www.lootedart.com/news.php?r=SBYXH2908751

Who was S.B.S. Slijper?

Court cases databases and APIs: art theft and Nazi looted art

Where to find detailed information about lawsuits involving Nazi-looted art?

a few online databases...

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Caselaw Access Project

https://cite.case.law

Suspicious provenance errors: Manet's Mellon

Mrs Kurt Riezler (née Käthe Liebermann, daughter of Max Liebermann) was previously mis-identified as Liezler

 Why does it matter? Because her family was persecuted by the Nazis and she herself was a refugee.

EDOUARD MANET

The Melon, c. 1880

Nazi-looted art: names of plundered collectors to verify in provenances

Books such as Was einmal war. Die enteigneten Kunstsammlungen Wiens by Sophie Lillie provide names of looted collectors