With four vacant ridings, why did Carney call just three byelections?

Global: The answer is a bit complicated, but the bottom line is that Liberal strategists would clearly have advised the prime minister that, given the unique political circumstances of the ridings that are currently vacant, the Liberals could give themselves a boatload more money to spend fighting off the Bloc Québecois in one vacant Québec seat by calling three byelections while depriving the BQ of cash it could use by holding off on that fourth by-election to fill a second vacant Québec seat…