Before the implementation of the Social Insurance Law, how did employees who participated in social security pay fees when they reached retirement age and worked for less than 15 years?

Before the implementation of the Social Insurance Law, those who reach retirement age and pay less than 15 years can pay in one lump sum. After the implementation of the Social Insurance Law, they can't pay in one lump sum, but need to pay as much as 15 years year by year. At present, it is widely practiced in various places that the annual payment is less than 15 years, and they can pay in one lump sum to 15 years.