More than half a century after their debut, the only links between Fleetwood Mac then and now are their rhythm section and their name. 50 Years—Don’t Stop is a well-curated overview of a group that began as a spirited British blues-rock combo and ended as a platinum-smooth global pop act. The real gems are on disc one (1968-1974), including the spooky “Black Magic Woman,” the melancholy balladry of “Man of the World,” the dynamically percussive “Oh Well, Pt. 1” and the “X-Files”-ish “Hypnotized.” A procession of great guitarists passed through the band before they settled on the lineup behind hits such as “Over My Head” and “Rhiannon” found on disc two.