So, do they deserve the title or have you or someone you know beaten them to it?

If you reckon your time is earlier get in touch and we'll investigate. You'll need to have unlocked your achievements whilst connected to Live¹ and have your profile visible so we can check the dates. If your achievement summary just says "Achieved" and doesn't display a date, then we can't check when you unlocked the last achievement so there's no point asking, sorry.