I was told that this is at the discretion of the station manager. I was trying to get out of EZE with 33 open in business and -33 (oversold) in coach. I figured I'm golden, they'll just tell those coach guys to get lost. WRONG! They randomly upgraded from coach into biz (apparently a lot of them weren't even medallion!), and NO nonrevs got on. Sleepinginairports.com is a good website... Be very careful if you ever see a situation like this, there are apparently no rules about coach > biz upgrades, especially internationally.