It's difficult to relate voltage to SOC, measurement resolution, accuracy and temperature will have an effect, since the voltage change for a 4 cell battery between 30% and 90% is only around 0.30 volts, (rested battery).
These numbers seem to be considered useful as a guide,
100% 3.42 cell 13.68 battery
90% 3.345 cell 13.38 battery
80% 3.34 cell 13.36 battery
60% 3.31 cell 13.24 battery
40% 3.30 cell 13.20 battery
20% 3.25 cell 13.00 battery
10% 3.20 cell 12.80 battery
Note there is a significant increase above 97%, at 97% SOC, 3.35 cell, 13.40 battery.
Thus even when charging to 100% once there is a small load,. the volts very quickly fall to 13.40 volts. It's also possible due to cell inbalance, the BMS stops charge before all cells are completly full.