All right, here's my current working theory:
This place was a stronghold of the Court of Tides, one of the Artists of which set up a time-loop-based defense around. The guy asking about couriers is asking about them because he was expecting advanced word of an attack on the stronghold by the Pale Warden. That attack eventually came and futzed with the time loop resulting in this constant debacle. The reason the children know about a more recent event than the Pale Warden vs Emperor of Tides is because the last Clerk who passed through told them of the Gossamer Blade's Duel. When that Clerk got trapped in the time loop, the Bureaucracy wiped the Village from the maps on-purpose to avoid losing any other Clerks.
Likewise, the Grandmother that's weaving is a red herring. This is just the natural result of practicing weaving for hundreds of subjective years within a stable time loop. All the people in the Village have some level of awareness that they're in a time loop and are part of the time loop proper, but outsiders aren't and can die after too many time loops from old age, which is why nobody wants to talk to us unless they have to. Nobody wants to take a chance on getting attached.
This all could be completely wrong, of course. It's just what I currently think is going on. . .