If someone comes to me after having achieved Dan rank in the same art elsewhere (i.e TSD to TSD or TKD to TKD), they are welcome to practice in my class (provided they have a good attitude). However, I have no legitimate claim to them as students, nor can I recommend them to test for higher Dan because they are officially considered students of the old organization. You cannot just leave one organization for another after having achieved Dan rank without certain etiquettes being followed.
So if someone moves from one part of the country to another and joins you, you won't consider them as students, likewise if their school closes down or instructor retires or dies that's it also? Do you 'allow' your students to train with anyone else? Are they allowed to cross train or are they your property totally?