  We investigate the impact of a variety of analysis assumptions that influence
cluster identification and location on the kSZ pairwise momentum signal and
covariance estimation. Photometric and spectroscopic galaxy tracers from SDSS,
WISE, and DECaLs, spanning redshifts $0.05<z<0.7$, are considered in
combination with CMB data from Planck and WMAP. With two complementary
techniques, analytic offset modeling and direct comparisons of redMaPPer
brightest and central catalog samples, we find that miscentering uncertainties
average to $0.4-0.7\sigma$ for the Planck kSZ statistical error budget obtained
with a jackknife estimator. We also find that jackknife covariance estimates
are significantly more conservative than those obtained by CMB rotation
methods. Using redMaPPer data, we concurrently compare the impact of
photometric redshift errors and miscentering. At separations $<\sim 50$ Mpc,
where the kSZ signal is largest, miscentering uncertainties can be comparable
to JK errors, while photometric redshifts are lower but still significant.
  For the next generation of CMB and LSS surveys the statistical and
photometric errors will shrink markedly. Our results demonstrate that
uncertainties introduced through using galaxy proxies for cluster locations
will need to be fully incorporated, and actively mitigated, for the kSZ to
reach its full potential as a cosmological constraining tool for dark energy
and neutrino physics.
