The society will always say that since the Russell and Rutherford days they have received new light. They say that it would have been impossible to have everything explained and understood immediately. Therefor things have been revealed gradually.
They then quote the scripture that says Jesus had more things to tell his followers but they were not ready at that time. (something like that)
There is no excuse though for teaching one thing then getting rid of it and then reinstating it again, which they have done with many things.