Perhaps this quote from the 2008 regs might help ?

Funny how nobody ever seems to read them


"Entries will be accepted in the following order of priority:-
1. Riders who finished in positions 1st to 30th in the corresponding race in 2007
2. Up to 30 additional riders in each race, based on previous fastest race laps
3. Up to 20 newcomers in each race
4. Additional riders selected at the discretion of the Organisers subject to a maximum of 85 entries in total in each race
Reserve Entries
For each solo race up to 5 reserve entries may be accepted in addition to the maximum of 85 confirmed entries. Reserves will practise with confirmed entries. Subject to qualification under SR 12, they will take the places (but not necessarily the starting numbers) of confirmed non starters up to a maximum of 85 starters per race. New numbers will be allocated to reserves when they are guaranteed a start, at the discretion of the Clerk of the Course. The first available will be given to the first named reserve in each race and so on as places become available."