Divide the Milky Way Mapper's spectra by its stars and DR20 averages at least two visits per target [1]. A second spectrum of the same star is what turns a parameter measurement into a measurement of change, because it can show whether the radial velocity moved. The thing an average does not tell you is the distribution behind it. Two-per-star is equally consistent with nearly every star observed twice and with a small subset observed many times while most were seen once, and the source material does not break that out. For a variability program, that distribution is the feasibility question, not the total.
The Black Hole Mapper adds spectra of about 500,000 stellar, intermediate and supermassive black holes [5], and the SPIDERS program supplies optical identifications for hundreds of thousands of X-ray-emitting active galactic nuclei, galaxy clusters and active stars, timed with the second eROSITA all-sky X-ray release [6]. The useful product there is the join. An X-ray position on its own is a detection; the same position with an optical spectrum behind it has a redshift and a classification.
A caution on totals. Emily Griffith, the SDSS-V spokesperson, described the release as over three million spectra of stars and galaxies along with 18 value-added catalogs [8]. Add the named subsurvey figures and you are already past 3.5 million [2], so that summary is a floor and not a sum, and anyone stacking subtotals from the press material will double count.
Currency is worth checking before building on any of it. The BOSS data in DR20 run through Feb. 2, 2025 [3], and the release paper appeared on a July 30 that the source does not year-stamp [9]. If that was 2025, the gap is 178 days; if 2026, it is 543 [3]. Either way, someone citing DR20 is citing the sky as it stood in early 2025.
Anne-Marie Weijmans, the survey's data products coordinator, treats access itself as a deliverable: the data should not just be publicly available but publicly usable, which is why the release comes with several platforms and worked examples for each [10]. That is an engineering claim, and the source offers no measurement of it. Juna Kollmeier, who directs SDSS-V, says the collaboration has already spent a week planning DR21 and DR22 and expects to need bigger computers [11]. Twenty-five years separate the Feb. 2, 2025 cutoff from the survey's start as a single 2.5-meter telescope pointed at the northern sky [4], and DR20 is where southern and northern BOSS spectra are reduced together with every previous phase [3].
