I'm sorry but I just said that I would read up on MQTT. I didn't say that I did didn't understand or believe the answer - just that I didn't know anything about MQTT and needed to read up on it! I think it's only fair that I do that before asking follow up questions that could be avoided by me doing some reading, don't you?
Peter, thanks for the information, presumably you meant "QOS Level 1 - at least once or better still QOS Level 2 - exactly once" rather than "MQTT.QOS_2_EXACTLY_ONCE or better still MQTT.QOS_2_EXACTLY_ONCE" in #2.
I wasn't aware anybody else had asked that question, If they have then I apologise for the duplication.