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tokens: inside the of each cluster. Many clusters have a so scarcely populated RGB that this parameter turns out to be null, which essentially points to negligible crowding in the cluster core compared to the environment of typical field-AGB stars. More populous clusters have a significant number of RGB stars, but their never exceeds 1.1 . At these maximum RGB densities, the magnitude bias turns out to be tiny (about mag), although the magnitude rms error (bottom panel of Figure 8 ) amounts to a very significant ∼0.12 mag. Assuming a Gaussian distribution of magnitude errors, the faintest among our candidate AGB stars could actually be TRGB stars (or real AGB stars slightly fainter than the TRGB) which entered into the AGB selection region just because of the photometric scatter. However, we verified that this fraction is very small: just 55 AGB candidates (shown in Figure 8 ), or ∼6 % of the sample, have a F160W magnitude compatible with it being a TRGB star scattered upwards by one rms. These cases include AGB candidates in dense globular clusters such as AP 1969 (B225-G280; Figure 4 ). Overall, these estimates of the cluster densities and crowding errors are quite crude and subject to many uncertainties: few RGB stars per cluster, no real fitting of cluster density profile, no real estimate of the likelihood of RGB stars being scattered into the AGB region, etc. Moreover, it suffices to examine Figure 4 to conclude that proper estimates of the effect of crowding would require extensive—and time-consuming—experiments of artificial star tests using the actual cluster images, or fully synthetic cluster tests. For the moment, we limit ourselves to making our estimates available in the final catalog, so that potential users can appreciate, with the help of Figure 8 , the chances that AGB candidates in a particular cluster are significantly affected by crowding. 2.6. C/M Classification with WFC3/IR Medium-band Filters We augment our catalog of cluster AGB candidates with estimates of their spectral subtypes where available. First, we use results from Boyer et al. ( 2013 , 2019 ), who performed an HST survey using WFC3/IR medium-band filters in 21 regions across the PHAT footprint, to classify their bright red giants as either C- or M-type. Their method uses the sensitivity of the filters F127M, F139M, and F153M to the presence of either CN + C 2 or H 2 O absorption features in the NIR. We cross-match our sample of 937 candidate AGB stars in clusters with the complete Boyer et al. ( 2019 ) catalog. We find a total of 59 robust matches, for which the differences between the catalogs are smaller than 004 in position, and smaller than 0.017 mag in both F110W and F160W magnitudes. All of them are classified as M stars. The lack of C stars is this small sample is not surprising, given the remarkable scarcity of C stars in M31, especially in its innermost regions (Boyer et al. 2019 ). Indeed the average C/M ratio across the M31 disk amounts to just ∼0.02. 2.7.