From 陈永贵 's promotion, it shows the greatness of 毛泽东.
陈永贵's contribution to China is huge. He solved the problem that had never been solved in the history in China: agricultural products always depended on weather. Once the weather was in bad condition, either dry or over raining, the nation was in the status of food shortage. Many people were hungary or died of starvation.
The experience from 大寨 helped China to build a good irrigation and drainage system that would prvent the agricultural products to be affected by the weather. Actually even today, Chinese agricultural products still depend on that system. With such a great contribution to the whole nation, who cares about his life history working with Japanese?
That is the greatness of Chairman Mao, who was more interested in the real contribution of the person to the country, not matter how famous or little he is. For instance, 大儒季羡林 very famous, but what is his real contribution to the country? 钱学森 is famous and he helped China building the 导弹航空航天 system. When great cultural revolution started, 钱学森 was immediately protected by the army.