I don't interpret the rules in such a way. The listed DC is for pass/failure, with progress and setbacks being adjudicated by the DM as situations permit.
If there's something that says the DM should set different DCs for progress and setbacks, I must have missed it.
Thats fine if thats how you choose to parse it.
The way i see it as not binary is they provide three to four distinct types of results for ability checks including contests... Progess, some progress with setback and no progress for std, adding in status quo for contests.
The DC for success fail are set by either the opposition or by the GM, so there is definitely the possibility and room for the GM to set different DCs based on whether he sees the "uncertainty" as "setback" or "success".
Consider the following case... An area might be rather rich in game making foraging even easy DC 10. But for areas around waterways where the game is still just as or more plentiful (would be DC 5) but certain aquatic threats attack humanoids. There the DC could be set at 15 or even 20 because the GM determines its the threat (setback) that is being rolled against.
Thats why i see it as trinary - the decision of is it rolling against the "setback" or rolling against the "progress" is really what defines and informs the DC choice.
A similar case could be a ruined room with stuff and possible treasure scattered about but maybe some unstable floor or structures at play. Depending on the setup, maybe the roll is "finding loot among the rubbke" or maybe its "finding loot pretty much given but do you do it without instability and collapse based setbacks"?
That decision by the GM should or at least could cause him to asdign different DC for the task and approach given.
So, in my games, its not a blind or binary DC check with setbacks as an option or factor only after the roll, but a trinary choice made before assessing DC.