Neither took the checker.
That's what I was looking for...Corum and Davis are each credited with winning the 500, although neither one actually took the flag in first place. Corum was relieved by Joe Boyer in 1924, and Davis was relieved by Mauri Rose in 1941. Corum competed in 6 races, and Davis in 4, but neither ever led a lap at Indy, even though they are listed as winners.
Some sleuthing on my part uncovered that Karn was right about Davis and Rose winning without changing tires...details on the 1924 race are more sketchy, so I can't comment on Corum/Boyer's tire usage.
Relief driving was fairly common into the late '60's, but the changeover to rear-engine cars with smaller cockpits made it more difficult. Today, it's almost unheard of, since the seats are molded to the driver's physique.
I didn't know just how to word this puzzle any simpler without giving at least part of the answer away...sorry if it was confusing. So, 2 points for GRAYWOLF and 1 for Ultrra...
Dan