Now I've always understood the shoulder to be BOTH the BUTT and PICNIC. Is that not true?
As I understand it, the butt is the upper portion (like the butt portion of a ham) and the picnic is the lower portion (like the shank portion of a ham).
I got it wrong?
The problem here is terminology of the butcher, store, and the end user. In the store they referred to cuts as roasts, but simply labeled as pork shoulder, a shoulder roast is not a whole shoulder.
A whole ham comes from the rear quarter, whereas a picnic ham come from the front quarter. They are whole cuts of meat. They are also referred to as "Whole Shoulders"
A whole shoulder cut with the shank -- or hock -- attached is called a "picnic", or "whole picnic" in the slaughterhouse. This cut is cheaper than most because it requires less cutting and butchering because it has more bone in it. Picnic hams usually come straight from the abattoir in a clean, cryovac'd package, all ready to go. It contains both the butt and the shoulder roasts.
Boston butt, or pork butt, comes from higher on the carcass above the shoulder blade and has lots of juicy, marbled fat. This is probably what most people buy when they purchase pork for making pulled pork. It's a versatile piece of meat that you can just as easily smoke, roast, or braise for home cooking.
Below the butt is the pork shoulder (roast), once the butt end is cut from the picnic you have a shoulder or shoulder roast. This cut includes most of the hog's front leg quarter, minus the butt end. Because the leg muscles work a lot more than the back, the meat is a little tougher, thus requiring a bit more time to coax out tenderness.
It can be confusing if you work with multiple sources. The slaughter house I use tells me the whole shoulder is a picnic, and that what I get when I order a case of picnics.