When an application register multiple times with GCM & UPS the devices receives duplicate notification for a period of time between 1 and 3 weeks. GCM returns UPS a field in the json response canonical_ids when a notification is sent to an expired device token.

Receiving this field should trigger an a cleanup/update in the UPS's installations list and the old token should be replaced with the new one. UPS should perhaps completely remove the old installation as it is not relevant anymore.

References:

1. https://developers.google.com/cloud-messaging/http-server-ref
2. https://developers.google.com/cloud-messaging/registration#canonical-ids