Father began to pay insurance from 1993. Why can only the payment after 2004 be found in the social security system?

There are many possibilities for this situation, but the fundamental reason lies in the network data of social insurance institutions in your area. Because the time when social insurance institutions in different places make personal data public online is different, the early data may not be entered into the network data, so of course it can't be found. Some areas regularly update the data of social insurance institutions, and do not keep the previous data. After this time, only the updated data can be found, but the previous data cannot be found. Of course, there are other factors. I suggest you go to the local social insurance agency to inquire and get a clear answer.