If you believe "handling at least once is enough as training" then there is nothing specific needed for training, isn't? It's like opening your new car's fuel tank hatch for the first time, you just need to read the manul for once in 1 minute. An average intellegent person can open the aircraft emergence hatch by reading the printed texts on it without any training, let alone a skilled baggage handler. Many incidents of smartass passenger opened emergence hatch are good evidence of "no training needed". This also includes refueling the aircraft. Pulling and pushing the aircraft is like experienced driver maneuvering a lorry of similar size from different brands without any prior training, the hooking up is standardized already.