Answer by @Brendan Jan 08, 2017 at 08:09 PM at https://community.playfab.com/questions/7619/linking-multiple-of-same-platform.html
Yes, you can have multiple iOS Device IDs all linked to the same account. Right now, we only show the one you most recently used to log into the account in the Game Manager and user account info query - that's something we'll be fixing in an upcoming sprint.
I having a problem to see all iOS device IDs that linked to the same account. May I know is there any way I can retrieve a list of all linked iOS device IDs, no matter from cloudscript / Client API / Admin API ?