The etymology of GULAG is: "the acronym of Гла́вное управле́ние исправи́тельно-трудовы́х лагере́й (Glávnoje upravlénije ispravítelʹno-trudovýx lageréj, “Chief Administration of Corrective-Labor Camps”)" emphasis mine, as it corresponds directly to the above, specifically the camps under the O.G.P.U. These are where those with harsher sentences were sent, as seen in the chart (3-10 years)