OEMs typically spend a lot of time and resources on quality assurance and testing to ensure that a given configuration of multiple devices will perform correctly.
When an OTA update is required, it is necessary to maintain full coherency of the system configuration. This means it is necessary to move from one known, tested, and fully verified state, to the next. It is not acceptable to end up with a mixed configuration with various devices in alternative states, as this would never pass the test.
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