I read somewhere that rollout isn't based off serial number. Sprint does a rollout on stages and gradually increases the number of phones allowed the update as time passes. Your phone has a certain percentage chance of receiving the update when you query, and as time passes,that percentage gets higher. This way if there were major problems they could catch it early before too many people get it. My understanding is that your phone is allowed one query every 24 hours and after that one, any further button mashing nets you the same results. Clearing the services might trick the servers into thinking you have not checked yet and basically resets your chances.
This is just something i read on a different message board, but it makes sense.
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