As a result, we cannot count your credits in Spain to benefit from free Medicare medical insurance. In addition, many countries have complex social security systems, for example. B which depend on the nature of the work. In these cases, a tabination agreement should set out very explicit guidelines and restrictions that might not apply in other countries. Example: U.S. agreements allow the U.S. Social Security Agency to add up U.S. and foreign coverage credits only if the employee has earned at least six-quarters of U.S. coverage. .