M. F. Skrutskie

TL;DR: The third generation of the Sloan Digital Sky Survey (SDSS-III) took data from 2008 to 2014 using the original SDSS wide-field imager, the original and an upgraded multi-object fiber-fed optical spectrograph, a new near-infrared high-resolution spectrogram, and a novel optical interferometer as discussed by the authors.

TL;DR: SDSS-III as discussed by the authors contains the first spectroscopic data from the Apache Point Observatory Galaxy Evolution Experiment (APOGEE), along with spectra from the Baryon Oscillation Spectroscopic Survey (BOSS) taken through 2012 July.

TL;DR: Data Release 13 (DR13) as mentioned in this paper is the first data release from SDSS-IV, which contains new data, reanalysis of existing data sets and, like all SDSs data releases, is inclusive of previously released data.

TL;DR: The most recent data release from the Sloan Digital Sky Surveys (SDSS-IV) is DR16 as discussed by the authors, which is the fourth and penultimate from the fourth phase of the survey.