Is the combined years of social security in the two places cumulative?

According to the query of French Open, the combined years of social security in the two places are not cumulative. When the payment is repeated in the same time period, the social security paid in one place in the repeated time period must be returned. So it is meaningless to pay social security in two places at the same time. The main purpose of social security is to obtain economic compensation and material help from the society to ensure the basic life when workers reduce or lose their labor income due to old age, unemployment, illness, work injury and maternity. Social security includes endowment insurance, medical insurance, unemployment insurance, industrial injury insurance and maternity insurance. Among them, pension insurance, medical insurance and unemployment insurance are all borne by individuals and units, while work injury insurance and maternity insurance are entirely borne by units, and individuals do not need to pay fees. Social security provides citizens with the right to get material help from the state and society in some cases, such as old age, illness, work injury, unemployment and childbirth.