First of all, I don't know the difference between stock, broth and bouillon in english (not my native language), but what I mean is when you cook for example a chicken carcass with vegetables for a couple of hours to use the liquid, discarding everything else. My question also applies for when you cook any other type of meat which haven't been pre-cook, meaning it will have quite a lot of fat remaining.  However, when you make your own stock, how much fat will there be in it? I'm mostly interested in the fat content after you've removed the "lid of fat" after refrigeration, but also immediately after sieving, if anyone has answer to both questions.  And naturally, I know it's hard to determine the fat content without doing an analysis, but I'm not calling for an exact answer on the gram, just if it's around 0–5 %, 5–10 %, or 10–20 % or whatever – just be as precise as you can.  When buying stock in the store, it usually says 0 g fat, but I guess they have some method of removing all of the fat, lowering the risk of it going rancid and increasing shelf-life. In my stock, I can see quite a lot of droplets of fat.  One way of attacking the question can be: Doesn't all the fat have to come up the surface ("the lid") since fat and water are unmixable? If fat is still in the broth, a) has it cooled down before all of it was allowed to rise (can be difficult in gelatin rich stocks)?, or b) can a stock hold fat in an emulsion? 
Shoulder is a tough cut. I think you will probably find it a bit chewy if you've cooked it at 190ºC for 52 minutes. In future, preheat the oven to maximum, place the lamb in a roasting tin, cover the tin with foil, put the tin in the oven, then immediately turn the oven down to 150ºC, and leave it for 4 hours. After that time, take it out of the oven and let it rest for 30 minutes or so. The lamb will melt in your mouth.  And yes, you can buy a bone-in shoulder at just about any supermarket, and they are usually tastier. Cook it as above and you will just be able to pull the bone out of the meat. 