You could just as well ask since when they had aquashuttles or a bridge intruder defense system. Heck, new things cropped up unexplained in TOS all the time -- new shipboard sets like the emergency manual monitor and McCoy's lab, new instruments on the bridge or engineering, etc. They didn't get spacesuits until "The Tholian Web." So if TOS got to add new details that we hadn't seen before, there's no reason TAS couldn't do the same. Wouldn't have been much of a continuation if it had been limited to what we'd already seen.