Look at who plays those opening frequently. If someone responds with the Slav in 80% of their games against 1. d4, and they're a GM, you can be sure they're a leading expert -- regardless of if they write on it or not.
Opening Specialists
Sort:
Nimzo - Kramnik, Karpov's old games
Slav and Semi-Slav - Shirov, Anand
Sicilian Taimanov - Mamedyarov, Movsesian
how about for the rest of the main openings: caro, french, ruy lopez, sicilian-najdorf, etc?
Who are the leading experts on openings such as Nimzo Indian, Slav defense, Semi-Slav defense, Sicilian-Taimanov, etc? It would be nice to know as it would help me in my study of master games.