Locating Phone w/ Find My iPhone When Login Name Changed on Icloud

Question

My  son had his iPhone 6 stolen and it was registered on Find My iPhone.  About 10 days after it was stolen, while we were periodically monitoring iCloud to see if it ever got turned-on, my son changed his login name & password on iCloud.  So now we has two devices (iPhone 6 & iPad) with the old name on them with corresponding passwords, and his iCloud account with a new name & a new password.
To add perspective on my question, even though the iPad had the old name & old password, it was located on his iCloud Find My iPhone map  & iCloud would indicate when the iPad was turned on or off. Just to confirm, his iCloud account has a new login name & new password.   What I'd like to find out is since there appears to still be a linkage between his iCloud account and his iPad, would it follow that there would continue to be a linkage with his iPhone 6 (old name/old password) and his iCloud account.  If the linkage continues, we would  continue to monitor his iCloud in case the phone gets turned on;  if not, we will of course just have to move on.   Thanks very much for any help with this. 

Answer 1

I've learned a lot about Apple Customer Service and this forum through the unfortunate theft of my son's phone.  First of all, the customer service people at Apple are poorly trained.  My first 4 calls during the theft resulted in totally different answers by 4 different people.  One techy from Florida was adamant that we would not receive an email if the stolen phone was connected to the internet via wifi/or 4g.  He, of course, was  completely wrong, and this is about as basic an issue as you can get with Find My iPhone. And I continue to wait, going on close to a week now, for what should have been  a fairly routine question from a "tier 2" or Senior Adviser as they're called, for an answer to our question.
When I stumbled upon this Apple "Support" Community, I was elated.  I thought, at last there's bound to be someone here who could give us some help, perhaps an Apple employee that hangs out here and  tries to "be there" for their customers.  Well, after waiting about 3 days and seeing that over 100 people have read my question, I am frankly surprised that not even one person has offered any help at all!   Based on my personal experiences with the Apple Customer Service Department and this  Apple Support Community, I am not impressed. 
I am very familiar with the way a good tech forum works and quickly learned this is not such a forum. I realized I had to go somewhere else to look which I did.  I found another Apple forum (not run by Apple btw),  and I posted the exact same question.   I received a reply within 20 minutes.   I suspect I will receive more throughout the day with the kind of advice and help I was hoping to get through Apple Customer Service and/or this Support Forum.
My reason for posting this comment to your support community  is to let other new people realize there are other much, much better places on the internet to look for help and support with their Apple  problems and issues.