isn't center mass the preferred target because 1.) It's big and easy to hit 2.) Holds a lot of vital stuff 3.) Hydroshock does really nasty things to organs even if you don't hit them?
1 and 2, Yes, 3, not so much. Hydro-static shock has been discussed, and in many circles, accepted to be a myth in regards to the average handgun wound. The human body is very elastic, and can absorb a great deal before the temporary wound cavity would increase the probability for incapacitation. If you are looking to generate shock trauma to the human body, better to start carrying a 12 gauge with slugs, or a rifle.
The way I have always been taught, shoot until the threat is over, or the gun is empty. Center mass is the biggest target (typically) that will result in an incapacitation, though I have hear from reliable sources that even a shot gun loaded with buck can fail to drop some attackers in certain situations.
All we can do is train for the most likely, and effective scenarios, and include a plan B,C&D, just in case the primary doesnt work.