Iam buying an xbox360,iam worried that the seller may sell me a older version of xbox360,how to differentiate?

iam buying from grey market pre modded xbox360. by the older versions i mean the core , pro and elite versions that were available in india and now only core and pro are available with completely different price tags. How can i differentiate b/w the newer core,pro and the older core,pro versions as date of manufacture cant be trusted .|||The only sure way in America is to check the power supply cord it should say 175 watts on it,but i am not sure if that applies in your country......I hope that helps|||It really shouldnt matter as long as u are able to get the most recent update for it after you buy it|||They wont sell you an old one unless your buying one from like gamestop.