Stranger takes place at the same time as the
Oddworld Quintology. The
Quintology doesn’t take place in Oddworld’s dark ages, it takes place after Oddworld’s industrial revolution. The Glukkons’ dark ages were their Alchemy Era when they suffered what Lorne calls a ‘spiritual meltdown’.
The quote at the end of
Stranger’s Wrath includes the dating 1868–1939 because
Chief Luther Standing Bear is an actual person to whom the quotation is actually credited. The dates are nothing to do with Oddworld, but the quote is everything to do with Stranger.