Wouldn't be better as a "guideline" instead of a "rule"?
Most associations/events that I have ever seen where there is such a “rule" pertaining to a lower and upper limit, it has always been worded that the "race shall not start when the wind strength is under 5 knots or over 20 knots, at the judgement/discretion of the officer of the day". Nothing about what the wind strength does during the race. After the start it is up to the sailors whether they continue to race or not, with no come back on the RC etc,