I wonder - if it sends duplicate notifications for each user that follows that user who moves per instance. For example, if 20 people on NCD follow his old account and then he migrates, each account may receive 20 notifications. Whereas if 50 people from Poast follow him, they get 50 notifications each. This could be tested, if you like. I've got time to help.

The reason I say this is because I only got about 10 notifications, but I saw other people get many more.