Apart from the previously mentioned inaccuracies, one thing I note:
I totaled the Burn and Remaining
Burn is measured near the nozzles in the engine.
Remaining is what's in the tanks.
In between you've got a bit of fuel in the pipeline. After shutdown you can 'see' this fuel pouring back by a slight increase in fuel quantity over a minute or so. I believe also the reason why FMC fuel onboard is more than adding the fuel gauges together.