Minstrel

I've looked around and can't find guidance on a specific question. When a boy transfers to another troop, what is the proper location of the unit's section of the merit badge blue cards? Should the unit where he earned the badge keep them, or should they be transferred to the new unit's advancement chair? In either case, should the other unit get a scan/photocopy? Is there a even a right/wrong to this, and instead more about what the boy wants?