Where once a board schedule may have consisted of between eight and ten meetings a year, in many companies the number of events requiring board in put and decisions has dramatically risen.
where在此引导让步状语从句，once为副词意为曾经，以前。where和once之前没有直接关系。关于once的这种用法，词典解释如下：You also use once to say that something happened at some time in the past.
I once investigated this story and I don't think it's true.
'Once I saw a shooting star here,' Jeffrey says.
When once is used with this meaning, it usually goes in front of a verb or at the beginning of a clause.