  We perform an extensive analysis of optical counterparts of Planck PSZ2
clusters, considering matches with three recent catalogs built from SDSS data:
AMF DR9, redMaPPer (v6.3) and Wen et al (WHL). We significantly extend the
number of optical counterparts of detected Planck clusters, and characterize
the optical properties when multiple identifications in different catalogs
exist. For Planck clusters which already possess an external validation, we
analyze the redshift assignment for both optical and X--ray determinations. We
then analyze the Planck Cosmology sample and comment on redshift determination
and potential mass mis-determinations due to alignment issues. Finally, we
inspect the reconstructed $y$ map from Planck and reason on the detectability
of optical clusters. Overall, AMF DR9 main (extended) finds 485 (511) optical
matches, with 45 (55) previously unmatched PSZ2 clusters, to be compared with
the 374 optical matches already present in PSZ2. 29 of the 55 previously
unmatched clusters do not yet have a followup in the literature. 18 of these
are found in more than one SDSS catalog with consistent redshifts. We provide
redshift and mass estimates for the newly matched clusters, and discuss the
comparison with the follow-ups, when present. We find good agreement between
the redMaPPer and AMF DR9 redshift determinations. From the Planck Cosmology
sample, we find 14 clusters which merit further investigation, and discuss
possible alignment issues for 9 of these clusters. After inspecting the $y$
map, we provide a list of 229 optical clusters not included in the Planck PSZ2
catalog but showing a prominent $y$ signal. We have further investigated the 86
clusters with Planck S/N $>4.5$ using the MMF technique (applied to the Planck
HFI maps), and were able to detect 20 new cluster candidates that are not
included in the PSZ2 catalog.
