Apple told Business Insider at the time: «The diagnostic data we've received from upgraders shows that for this small percentage of users experiencing the issue, we're seeing a more than 80 % reduction in iPhone 6s and over 70 % reduction on iPhone 6 of devices unexpectedly shutting down.» (businessinsider.com)
The first is simply to boost your holdings in the international funds recommended for Upgraders on page 122. (soundmindinvesting.com)
Cook noted that out of the total, active iPhone user base, 20 percent have upgraded to the new iPhone 6 and 6 Plus, so there's «some headroom» for plenty of upgraders in the future. (zdnet.com)