  We present the probability distribution of the systematic errors in the most
accurate, high-latency version of the reconstructed dimensionless strain $h$,
at the Hanford and Livingston LIGO detectors, used for gravitational-wave
astrophysical analysis, including parameter estimation, in the last five months
of the third observing run (O3B). This work extends the results presented in
Sun et. al (2020) [1] for the first six months of the third observing run
(O3A). The complex-valued, frequency-dependent, and slowly time-varying
systematic error (excursion from unity magnitude and zero phase) in O3B
generally remains at a consistent level as in O3A, yet changes of detector
configurations in O3B have introduced a non-negligible change in the frequency
dependence of the error, leading to larger excursions from unity at some
frequencies and/or during some observational periods; in some other periods the
excursions are smaller than those in O3A. For O3B, the upper limit on the
systematic error and associated uncertainty is 11.29% in magnitude and 9.18 deg
in phase (68% confidence interval) in the most sensitive frequency band 20-2000
Hz. The systematic error alone is estimated at levels of < 2% in magnitude and
$\lesssim 4$ deg in phase. These errors and uncertainties are dominated by the
imperfect modeling of the frequency dependence of the detector response
functions rather than the uncertainty in the absolute reference, the photon
calibrators.
