Who are the real authenticators?

You have a Picasso, with a certificate of Gallery ABCD , famous gallery in Beverly Hills!
What is the value of that certificate of authenticity? Nothing.
Here is a short list of experts for some major European artists, who are the unique authorized authenticators:

Picasso: Mrs. Maya Picasso and Palau Y fabre for early works
Van Gogh: Comite Van Gogh
Degas: Mr. Brame & Mr. Lorenceau
Chagall:Comite Chagall, Mr.Prat  
Miro:Les Amis de Miro, and Mr. Jacques Dupin
Dali: Mr. Descharnes
Cezanne: Mr. Reff
Seurat : Mr. Philippe Brame
Sisley : Wildenstein Foundation
Gauguin : Wildenstein Foundation
Matisse : Mrs. Wanda de Guebriant
Malevitch : Mr. Andrei Nakov
Kandinsky : Mrs. Vivian Barnett
Nolde: Mr. Martin Urban
Leger: Comite Leger
Poliakoff: Archives Serge Poliakoff
Pissaro: Comite Pissaro
Modigliani: Mr. Christian Parisot
Boudin: Mr. Schmit
Picabia : Mrs. Olga Picabia
Utrillo: Mr. Fabris & Mr. Petrides
Pascin: Mr. Abel Rambert
Morisot: Mr. Yves Rouart
Valtat: Mr. Louis Andre Valtat
Foujita: Mrs. Sylvie Buisson
Toulouse-Lautrec: Mr. Brame
Turner: Mr. Martin Butlin
Van Dongen: Mr. Belier
Viera da Silva: Mr. Jaeger
Nattier: Mr. Baillio
Oguiss: Oguiss Myoko
Millet: Mr. Aubry or Mr. Lorenceau
Henri Martin: Mr. Cyrille Martin
Magritte:Mr. Isy Brachot
Georges Carrey: Mr. Arry Van Weyenbergh