I'll state again that basing SoC on voltage for a battery under load is an imprecise estimate of SoC.
But Lincoln doesn't have to do it that way. They know how many mAh have discharged from the battery since the last charge. Just like your cellphone, they track the history of net mAh discharged from full to empty, so they know the effective capacity of the battery. When you're cellphone says 50% remaining, that's means it's consumed half of its effective capacity. It's the same with the Nautilus.
TLDR; Your Nautilus SOC reported by Lincoln is a more precise estimate based on charge collected vs discharged, not mere voltage.