Bi carb testing is done BEFORE racing. It's all about timing, too early and the effect wears off, too late and you guessed it.
It says something about how inept the Racing Vic. policing was obviously. They supposedly randomly test 30 odd per meeting but these dirty rotten cheating Smeerdons were keeping an eye out for Stipe's number plates and apparently had inside knowledge of who were going to be tested that day among other things.
If this happened here, under the Crimes Act, the perpetrator's could be charged with fraud, not just warned off as these grubs have been, along with meaningless fines which they simply won't pay.