Apognophos
Honestly I don't think this is a big doctrinal problem. For instance, as a number of posters here have pointed out, this period could be likened to the 120 years before the Flood, during which Noah supposedly warned his generation of the coming judgment. So far, that pre-Flood system has gotten 20 years' more warning than ours has, if the warning started in 1914. Mind you, I'm leaving aside the point that Noah's supposed preaching work is not mentioned in Genesis; I'm simply answering this from the perspective of JW doctrine.
You could use that argument with anything the WTBTS teaches. That is, 'I don't think this is a big doctinal problem'. Then you likened it to Noah's day. Fortunately, you qualify it with Noah just 'supposedly' warning his generation of the coming judgement. That was not the job that Noah was instructed to do. He was given the 120 years in order for him to fulfill God's requirements of building and stocking the Ark. In doing this he was declared a righteous man by doing God's will. The judgement had already been made and only Noah and his family were to survive. There was no coming of judgement. It was a time of preperation, not of a preaching work.