As I can see regularly, when we ask a question Q to the WTBTS, the answer was :
1910 : A
1930 : B
1940 : A and B
1950 : A but not B
1960 : B but not A
1970 : A
1980 : C
1990 : D
2000 : B
2010 : B and C and D but not A
And in 2015, the answer looks like : "in the past our publication said some things, but now twe know that the answer is : maybe A, maybe B, maybe C, maybe D, maybe a mix of them."