As IB says its down to honesty, verification is checking ring number, wing mark etc and liberating the bird at its home loft and watching it re-enter the loft.
But there is nothing to say the bird hasn't been collected from another location 100miles away over night etc.
How many birds have 2 homes?
I have heard of many birds stopping of at regular lofts enroute for a rest and then heading for home. If a bird was doing this regularly the owner could actualy wait at the stop off point for the bird, clock it and drive home with the bird which could then be verified at the home end!
Makes you think!
Phil