If you look at the calculator on yeastcalc.com, you can see what volume of starter you need to get 422 billion from 1 vial (100 billion per vial) and stirplate. You'll find that you'll need close to 4 L to get the population growth to hit your target. Mrmalty tends to optimize for smaller starter volumes by bumping the initial size of yeast. That is, you can get to 422 with 2 vials with less starter volume.
To be fair, I haven't found any studies that have formulas for determining yeast growth with stir plates to see how those two calculators arrive at thier growth projections, but I have confirmed that they both agree with starter sizes if you match the number of vials in mrmalty into the initial pitch size at yeastcalc.com