  The theoretically expected amplitude of the associations of background
quasars with foreground galaxies as a result of gravitational lensing has been
updated in this paper. Since the galactic matter alone yields an amplitude of
quasar overdensity smaller than that observed, a special attention has been
paid to the examination or re-examination of the uncertainties in the estimate
of the quasar enhancement factor arising from the cosmic evolution of galaxies,
the core radius and velocity bias of galactic matter distributions, the
clusters of galaxies, the obstruction effect by galactic disks, the non-zero
cosmological constant, etc. Unfortunately, none of these factors has been shown
to be able to significantly improve the situation, although a combination of
some effects may provide a result that marginally agrees with observations. It
is concluded that the quasar-galaxy association still remains to be an unsolved
puzzle in today's astronomy, if the reported quasar-galaxy associations are not
due to the statistical variations and/or the observed quasar number counts as a
whole have not been seriously contaminated by gravitational lensing.
