Rarity labels are the game's own tier names (Common, Rare, Guaranteed, etc.) taken directly from its loot tables — not invented percentages. Some items are
Tier-scaled instead: their real chance follows a curve tied to your effective loot stage (rarer early, common once you outlevel that tier, sometimes rarer again after) rather than one flat rate, so a single label wouldn't be honest.
Biome matters more than character level for these specifically — standing in Snow multiplies your loot stage by 2.5x, Wasteland by 3x, confirmed directly from the game's own biome data (see
World & Biomes) — so a Tier-scaled item you think is out of reach may already be common the moment you cross into a harder biome. 138 Twitch-integration-only containers are excluded — this covers normal gameplay containers only, 201 of them.