Indeed Mat.24:14 it is reffering only to the first century. And that generation lastet 32 years!!! On the contrary WT's it seems that there is no end to it. If we start from 1878 the SECOND teachning that Christ was supposed to come invisibly(there is also the first date 1799 that in the begining Russel used to believe, but we won't mention that) we have 131 years of failed expectations regarding the generation and the preaching work.
Besides there are places in the world that people DONT have a clue about JW's the American cult.Just to mention few countries that indeed the Good News(of the WT) haven't been preached like the way is done in western countries or not preached at all.
China: Population 1.200.000.000
India: Population 900.000.000
Other countries like Pakistan, Indonisia, Irak, Iran, Saudia Arabia, Egypt, Maroko, Syria, Bagladesh, Thayland, Libya,Turkey, basically this countries are more than 4 billions, and in the Muslem places WT cannot preach.
So the good news have not reached yet to the entire world. Besides did Apostle Paul preached at that time to the American natives or to the Inkas and Mayias, or in China or India?