Hi, my parents have worked in the US for over 15 yrs, and have had their GC for over 10 years. They have paid taxes each year for all of those years, and contributed to social security so that all their credits are now complete in terms of retirement. now they're looking to move for a few years (indefinitely) to another country, and they're looking to give up their green card. if I'm a US citizen, and they give up their green card, and at some point in the future i help them re-apply for a green card, will it still be in the system that they've completed their contribution to social security and they can still receive their social security retirement benefits from before they gave up the green card? or will they lose all the points they've accumulated and have to start from the beginning again? Thanks in advance!!!