I sometimes tell him the story of his life, details of what he did in his working life, stories of his friends, the adventures he undertook.

That seems like a good thing for people to do for themselves. Make a bunch of videos recounting your life. Useful if the mind falters, and useful even if it doesn't falter so much. Our recollections no doubt wander over time. Even without any claim about which recollection is more/less accurate, they're all useful data. At least to someone looking to reminisce.