A registry master data management approach is primarily employed as a central index linkage to the concept of master data, in that the master records are authored across the different systems, but with a linkage that is commonly referenced by the different systems as an external key.
Just as for transactional and coexistence approaches, the authoring remains in the satellite systems and at best, the registry serves as a skeleton that contains essential attributes of the master that are common across the systems.
Often the data is simply used for interrogation, lookup, or reference.
Because you are working with a skeleton of definition, there is relatively loose control over the customer master because this point of reference only provides a sliver of definition to the customer master.
External keys become useful if held.
The Skeleton Key becomes an authority of sorts, but only if it is referenced in the peripheral systems, as an external key for referencing and minimization of duplication.
This approach is fast to implement and provides some degree of central and distributed master data governance if all participants agree the skeleton can operate as a central reference point or authority.