It looks like Google may have lifted the de-authorization limit for Google Play Music8
For most people, a limit like this would not pose much of a problem, except that if you were to reset your device, Google might create a duplicate profile in Google Play, taking an extra spot out of ten available to you.
Today, word got out that perhaps Google has changed its mind again, as we are seeing note around the internet that folks (including some here at PhoneArena), have been able to de-authorize more devices out of their Google Play Music device management, even though they had previously hit the four device limit earlier this year.
What is not clear is if this is a change in policy, a grace period, or a software glitch, because as far as we can tell, the four device de-authorization limit is still written in the policy on Google’s support page. In the event that it is a glitch, and you want to do some housecleaning, this may be a good time to dig in and clear things out. Simply open Google Play Music on your Android device, select “Settings,” then “My devices.”
Let us know if you were able to de-authorize more devices if you had previously hit the limit.
source: Android Central