The story line of this episode has points which do not stand up to close scruinty. For examaple, No.6 is able to log that he was at sea for twenty-five days, this dispite being in a state of collapse for the remainder of his voyage. Because on;y 18 days are actually recorded in his log.
No.6 provisioned his sea-going raft. He took with him a copy of The Tally Ho upon which he wrote his log. He took photographic evidence of the village. A jam jar, string, a piece of round cork, a packet of village darning needles, two wooden rulers, and a loudspeaker, and a pencil, from which he constructed a homemade compass. Yet No.6 failed to take any warm clothing with him. In the reality of the situation, No.6 would have been wet through by the end of the first day. Wet through, cold, the salty sea water making his clothes stick to his skin. And being open to the elements as he was, No.6 would very soon be suffering from hypothermia! We have to face facts, that there is really no-way No.6 should have survived that sea voyage of his!
I suppose one explanation of Many Happy Returns might be, that obsticles can be overcome, by someone who never gives up, and so one day must surely succeed.