An event can be run using "single certificates"

If it is considered desirable at a particular event to ensure a sailor cannot choose the best configuration to suit the prevailing conditions, the event organiser can issue a Notice of Race, and a Sailing Instruction, requiring a certificate to be lodged at some prescribed time ahead of the event and to use the boat in that configuation. This also prevents owners of multiple boats from choosing which boat to use at the time of the race.