This file *IS* what the soak users got as their update.
So, if Motorola decides that they want to keep working on the update and release an even newer one later, instead of pushing 5.6.890 to the masses then they will have to have an upgrade process for the soak users which have already updated to 5.6.890.
I know when I was debugging the "check_for_upgrade" service, it submits your build version when it performs the upgrade check, so the response back is personalized to your current build.
So the process goes like this for 2 different users:
User A(running 5.5.959) checks for upgrade and gets the verizon.en.US.5.5.959->US.5.7.0-update.zip (sends I'm verison 5.5.959 receives 5.7.0)
User B(running 5.6.890) checks for upgrade and gets the verizon.en.US.5.6.890->US.5.7.0-update.zip (sends I'm version 5.6.890 receives 5.7.0)