The performance and longevity of dough is largely a function of the amount of yeast used in the dough and the finished dough temperature. Finished dough temperature is a function of the room temperature (which is fairly correlated with outdoor temperature), flour temperature, water temperature and the friction factor of your mixer. Based on what you have said, if I had to guess, I would say that you are perhaps in a part of the country where it is now cold. Ideally, in a home setting where you are using a standard refrigerator, you want to shoot for a finished dough temperature of around 75-80 degrees F. I use an infrared thermometer to measure finished dough temperature but before I purchased that unit I used a simple instant read digital thermometer. A simple Google search should turn up many inexpensive models that should work. You can also use an analog thermometer if you already have one.
When using ADY, you should use only use a small amount of the formula water to rehydrate the ADY. Technically, that water should be around 4-5 times the weight of the ADY. That comes to a few tablespoons. The water should be at a temperature of around 105 degrees F and the ADY should be allowed to rehydrate in that warm water for about 10 minutes. The rest of the water should be at a temperature to achieve the abovementioned finished dough temperature of around 75-80 degrees F. If you tell me your room temperature where you live, and the outdoor temperature as well, I might be able to come up with a water temperature for you to use. Once rehydrated, the ADY can be either added to the rest of the formula water or to the other ingredients in the mixer bowl. The salt should be dissolved up front in the part of the formula water that was not used to rehydrate the ADY. It can also be added to the flour.
Your use of 1/2 teaspoon of ADY comes to around 0.61% of the formula flour. If you achieve a finished dough temperature of about 75-80 degrees F, with that amount of ADY I think you should be able to get about two to three days of cold fermentation before using the dough to make a pizza. It might be a little bit longer in your case because you kneaded your dough for 10 minutes, which is fairly long for a dough ball that weighs a little over 18 ounces. What you want to look for as you monitor the dough's performance during cold fermentation is the formation of fermentation bubbles at the sides and bottom of your storage container. For this reason, I suggest that you use a glass or transparent dough storage container so that you can see the fermentation bubbles develop. Those bubbles may be sparse after about one day in the refrigerator but should form the next day thereafter and increase further with time. The presence of spotting in the dough does not necessarily mean that the dough has overfermented. I think it is unlikely that you will see such spots develop to any significant degree with the dough formulation you are using for a dough that is cold fermented for only a few days. I have made doughs that have cold fermented for over 20 days, and the spots take five or more days to start to appear. The dough even then is not overfermented and can be used to make pizzas.
If you would like to read about the symptoms of an overfermented/overproofed dough, you might read Reply 36 at http://www.pizzamaking.com/forum/index.php/topic,11989.msg112445/topicseen.html#msg112445
In your case, you might also want to increase the hydration by a percent or two since your All Trumps flour can handle the higher hydration. If your All Trumps flour is also bromated, that, together with the higher hydration, should produce a better oven spring. The oven spring will also benefit from a high oven temperature of around 550-575 degrees F if you can achieve that. I think I would also reduce the knead time to around 7-8 minutes if you can get a smooth, cohesive dough ball in that time.
I think if you adopt the above measures, you should see improvement and consistency of results. If not, note what you do in detail, and come back for further advice and diagnosis.