OP was questioning whether Landau’s method of identifying the most gifted students actually selected for successful physicists: “It makes me wonder of the 43 s

OP was questioning whether Landau’s method of identifying the most gifted students actually selected for successful physicists: “It makes me wonder of the 43 students who passed, how many achieved significant breakthroughs or Nobel prizes?” So yes, it is selection bias by definition, but the point is that the method of selection worked. Most other professors at the most prestigious schools in the world could only dream of advising anything close to Landau’s academic descendants.