Why 99%? Because until the cheque is with the pilot, nothing is 100%
Why a date 'window'? Swimming the Channel is not as straight forward as just getting in the water. The pilots all arrange date windows for their swimmers, to allow for better chances of good weather conditions. The pilots further book up to four swimmers for this window, with each swimmer being allocated a swim position, 1, 2, 3 and 4. On the first suitable day, the pilot will contact swimmer #1, and offer them the chance. If they say no, for whatever reason, swimmer #2 is offered the chance, and so on.
I am swimmer #1 for my allocated dates (which could, potentially, actually be before or after that date window - it's complicated!)