Find the Apple ID my Device is registered with
I have multiple Apple devices, but only some of them are listed on http://supportprofile.apple.com/.
In fact, my two main devices, my 2011 MacBook Pro (which came from the apple refurbished store) and my iPhone 4 (which I got from a friend in exchange for a Nexus S, yey) are nowhere to be found, and if I try to register them, the site says they're already associated with another apple id. How do I find out which one that is?
I am going to ask that friend to check his device list and possibly remove the iPhone from it, but what's with the MacBook? There is no way for me to find out who possessed the MacBook before it got sent into the refurbished store.
EDIT: The friend removed the device from the list and I could register it now. The question about the MacBook remains.
MacBook Pro, OS X Yosemite (10.10.3), 13'' Early 2011