A little background history on the mail system that was used in Wings of Change.
In Balto 3: Wings of Change, Balto's son Kodi, and three other dogs (Dusty, Kirby, and Ralph) are used in a dog team. They have the important role of delivering the mail from their small Alaskan town of Nome to another (White Mountain) and back again.
But something caught the attention of a few fans with a keen eye: Why does the post office say 'U.S. Post Office' when the film takes place in 1928 and Alaska isn't even an official state yet? How is this possible? Is it a blooper? To answer this question: No, it is not a blooper at all.
Thanks to the town of Sitka in the territory of Alaska recieved its first U.S. Post office in 1867. The mail was transported by the use of sled dogs (which was the mode of transportation used by the Native People that also lived there). At first in Alaska, it was not very populated (except for the Native Alaskans) until the Klondike Gold Rush in 1897-98, in which people would pass their mail to someone that was heading for a certain direction in order to deliver messages. This continued until the mail services became more organized by 1912, when Alaska was ruled by a territorial government.
Of course, the diphtheria run of 1925 took place during this time period of territorial rule; many of the mushers used in the serum run were actually mushers for the U.S. Post Office! Unfortunately, by the late 1930s, the dog sled mail teams were being replaced by the flying creatures known as airplanes. Even though air delivery was more reliable in the snowy weather, dog sleds were still used to transport mail from one airfield in a big town to another. So, what Balto predicted in Wings of Change about planes taking over the jobs of sled dogs was true . . . kind of.
Near the year 1938, the Postmaster General made a new system called 'emergency mail' (people would make trails and places for dog teams during their journey and also hired more mushers (also called mail contractors) to deliver mail without traveling for too long). This continued throughout the Second World War; mail traveled mainly by dogsled, even though the U.S. Congress changed some of the Postmaster's original plans, making winter mail travel only by dog sled (even if airplanes were available). This made the mail take much longer to deliver from place to place . . . sometimes it took as long as three months to recieve your mail!
In 1959, Alaska became part of the United States and, soon after the year 1963 marked the end of sled dog mail when an airplane took over the last scheduled route.
Although the dogteam U.S. Mail Service is officially over, sled dogs are still used as a mode of transportation and for sport (such as the Iditarod (1973), which follows the path that the mushers took to deliver the medicine to Nome in 1925). However, dogsled mail deliveries are still done for special annual occasions, such as the Iditarod (a special letter that teams carry throughout the length of the race; the top five racers have their letters put up for auction to raise money to help fund the Iditarod race committee) and a special course called the Yukon Quest (a difficult path from Whitehorse in the Canadian Yukon Territory to Fairbanks, Alaska).