Eras
An era is not a decade. It is one career's full span: a player whose career total reaches 72 Legacy Index — four perfect seasons' worth — defines the era that runs from the first season they scored to the last one they did.
Four careers have cleared that bar: Michael Jordan (115), LeBron James (109), Magic Johnson (83), and Tim Duncan (79). Kobe Bryant misses by two points and Larry Bird by three. Shai Gilgeous-Alexander is at 33 and still adding, so his era carries a question mark until the number settles it.