For a start no-one is actually saying that your MFT needs official calibrating every 12 months, especially if you are conducting your own regular calibration checks at home.
What you should get back from an accredited calibration lab, is a certificate showing the actual values shown by your meter, against ''Known'' values its been tested against. All test equipment have resolution and tolerance criteria. Good labs will generally tweak your kit if just outside a given tolerance on a certain range. Even if they don't, they will 9/10 contact you while your meters on the bench, giving you the facts of what's been found, if you need a replacement component part, or needs in depth adjustments etc, and advise of any additional fee's before carrying out any work. Any additional work/parts that is agreed, will carry a warranty.
Actually many of these labs are a very competitive alternative to sending your meter back to the manufacturers for repairs etc. In fact many of them being accredited by virtually all the better test equipment manufacturers. I doubt if your average ''Mobile Mick'' is officially accredited by anyone but himself...