how does Krakauer know that in 1992,"six people in three separate parties happened to visit the remote vehicle on the same afternoon"?

Yutan Constructon Company brought the bus in to house construction workers who were upgrading the trail into a road.

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Here’s an excerpt from "Into the Wild" explaining the bus:

"The trail was blazed in the 1930s by a legendary Alaska miner named Earl Pilgrim; it led to antimony claims he’d staked on Stampede Creek, above the Clearwater Fork of the Toklat River. In 1961, a Fairbanks company, Yutan Construction, won a contract from the new state of Alaska (statehood having been granted just two years earlier) to upgrade the trail, building it into a road on which trucks could haul ore from the mine year-round. To house construction workers while the road was going in, Yutan purchased three junked buses, outfitted each with bunks and a simple barrel stove, and skidded them into the wilderness behind a D-9 Caterpillar.

The project was halted in 1963: some fifty miles of road were eventually built, but no bridges were ever erected over the many rivers it transected, and the route was shortly rendered impassable by thawing permafrost and seasonal floods. Yutan hauled two of the buses back to the highway. The third bus was left about halfway out the trail to serve as backcountry shelter for hunters and trappers. In the three decades since construction ended, much of the roadbed has been obliterated by washouts, brush, and beaver ponds, but the bus is still there.

A vintage International Harvester from the 1940s, the derelict vehicle is located twenty-five miles west of Healy as the raven flies, rusting incongruously in the fireweed beside the Stampede Trail, just beyond the boundary of Denali National Park. The engine is gone. Several windows are cracked or missing altogether, and broken whiskey bottles litter the floor. The green-and-white paint is badly oxidized. Weathered lettering indicates that the old machine was once part of the Fairbanks City Transit System: bus 142. These days it isn’t unusual for six or seven months to pass without the bus seeing a human visitor, but in early September 1992, six people in three separate parties happened to visit the remote vehicle on the same afternoon."

On September 6, 1992, three moose hunters managed to get across the flooded Teklanika River and arrived at the bus, where they found "a guy and a girl from Anchorage standing fifty feet away...looking kinda spooked." A "real bad smell" came from inside the bus, and a "disquieting" S.O.S. note was taped on the door. Upon investigation, the hunters discovered the body of Chris McCandless inside the bus, huddled in a sleeping bag. He had been dead "for two and a half weeks."

McCandless's remains, along with a camera, the note, and a diary, were removed from the bus by state troopers.

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