I, too, was at WDW last month during the Epcot fireworks' testing. I was staying on the 5th floor of the BCV, with an Epcot view, and was returning from a late night swim with my daughter when we bumped into a CM who was slipping a piece of paper under our door. I asked him what was up and he told me about the fireworks' testing. The testing lasted almost an hour, with fireworks being shot into the air every minute or so. I was surprised at how long the testing went on and even watched some of it from my balcony. I had friends who were staying on a different floor of the BCV, with a different view, and they told me that they did not get a letter from the resort regarding the "noise" that they had heard that night. They actually called down to the Front Desk to see what was happening with the noise. So, it seems to me, that maybe only those rooms with Epcot views got the fireworks' notice??
In regards to "other" fireworks over at the MK, when people are getting married via Disney's Fairy Tale Weddings Department, one of the wedding add-on's is a custom fireworks' show. The cost is several thousand dollars for a minimum of 2 or 3 minutes of fireworks. Most folks who choose that expensive add-on only buy the minimum, so if you've seen unexplained fireworks while in the MK area, it could be the finale to a Fairy Tale Wedding. The photographer poses the happy couple outside (the usual spot is behind the Wedding Pavilion), while a Fairy Tale Weddings' Cast Member radios the "GO" signal to the fireworks technicians. With timing like that, a perfect photo is taken of the newlyweds kiss with fireworks bursting in the background. As you can imagine, it makes quite a photo.