I mixed a bunch of colors awhile back. Since the ink reacts differently depending on any number of variables (how much ink you put on the press, temperature, paper color, how well you've cleaned the press, among a host of other things), I tend to undermix the ink a little bit so I can make color adjustments on press.
PMS 382 today is case in point. The bottom test print is the original 382 I mixed, which tested almost the right color the day I mixed it, but today it was not quite blue enough. It's also on pearl white, which adds its own amount of yellow. With just a touch of process blue mixed on press, I get to the exact color on top:
I use this method mostly because with colors like this, if you add too much blue the first time around, it takes A LOT of yellow to get it back to where you want it to be, and then you're stuck with way more 382 than you really intended.
Back to printing!