According to some research I've been doing:
''The MRI works with an accuracy of +or - 1 which means if you are a year over age it might not be detected but if you are above that limit there's a good chance you will be caught.''
This would explain your friends 1 year discrepancy and also goes a long way to prove why the supposed 7 years that Freddy Adu is overage is absolute tripe. And also why it has never been picked up by a major news source nor have we ever seen any credible evidence to support this claim.