image. Inspection of the $K_{\rm S}$-band image over COSMOS reveals that all selected massive galaxies are single, isolated objects, including C1-23152, showing no obvious signature of the two knots. If the photometry of C1-23152 is equally affected by the two knots at all wavelengths, the shape of its SED would not be affected, and the resulting stellar mass would be smaller by $\sim0.05$ dex, not changing the results of this paper. On the contrary, if the contribution of the two knots changes as a function of wavelength, the observed SED would change accordingly, making it harder to predict how the derived stellar mass would be affected. A rough estimate of this effect was derived by re-fitting the observed SED of C1-23152 after assuming that only the optical fluxes are affected by the two knots. The resulting stellar mass is only $\sim0.03$ dex smaller than that estimated with the current photometry, implying that the derived stellar mass for C1-23152 is not likely to be significantly biased by the two knots. We therefore conclude that none of the observed objects seem to be affected by blending issues, which might have resulted in systematically biased stellar mass estimates. Higher spatial-resolution NIR imaging is 