Pleione is drifting toward Atlas: 5.0 arcmin apart now, about 8.6 arcmin 100,000 years ago
scripts/pleiades_lost_sister.py. Three estimates of Pleione's motion relative to Atlas: Hipparcos (3.0 mas a year toward Atlas), Gaia DR3 (1.5, but Atlas's Gaia measurement is poor, RUWE 4.1), and the long-baseline motion from their positions in 1991 and 2016 (2.2 mas a year, the most reliable for binary stars). Running these backwards: 100,000 years ago the gap was 7.4 to 10.0 arcmin, best value 8.6; 40,000 years ago about 6.4. Norris and Norris give 8.4. The geometry in their paper is right.
How it connects
This clue from nature supports this hunch
The lost-sister stories date from 100,000 years ago, when Pleione stood clear of Atlas the geometry in the paper is right
This clue from nature is a clue for
Why do so many cultures call the Pleiades 'seven sisters' and tell of a lost one?
This clue from nature we read it in
Hipparcos new reduction (van Leeuwen 2007), VizieR I/311; Gaia DR3 archive; SIMBAD V magnitudes. Used by scripts/pleiades_lost_sister.py
This clue from nature came from this step
Checked the 100,000-year 'lost Pleiad' claim with star catalogues