I wonder who the well organized network could be, and I doubt that it is only in French museums

A state-owned French art museum has discovered that more than half of its collection consists of worthless fakes and experts fear that other public galleries may also be stuffed with forgeries.

An art historian raised the alarm after noticing that paintings attributed to Etienne Terrus showed buildings that were only constructed after the artist’s death in 1922.

https:// www.telegraph.co.uk/news/2018/04/28/french-museum-discovers-half-collection-fakes/

Detectives suspect that other museums may also contain large numbers of forged works attributed to southern French artists.

A source close to the investigation said: “We know there have been a lot of forgeries circulating and we believe a well-organised network was behind this."