My grandmother[1] was a political prisoner and her favourite pastime while in prison was poetry. Since the inmates weren't allowed to have any possessions, not even a strip of paper, she composed poems in her head. She later published them in a poetry collection and I know people who memorized the entire collection. She herself had a phenomenal memory for poetry. Her friends would often call and ask for her to tell them the lyrics of old songs and poems, and even in her late 70s she never failed to answer their request without consulting her library. My mum once challenged her and asked her to recite the 50 minute-long Máj[2]. If she weren't interrupted after 10 minutes, she probably would have recited the entire thing. She was able to memorize a poem after hearing it just once and it seemed that she retained poems indefinitely. I don't know whether this talent was the result of 6 years in an environment where memory is the only means to persist information, but it seems likely that it played a role.
Another less impressive anecdatum is my own experience of about a year with a phone that couldn't remember phone numbers. In the beginning I memorized numbers out of necessity. By the end of the year I had a mental address book of about 30 numbers and new numbers could be added effortlessly. The bewildered looks of people giving me their number without me pulling out a phone to write it down were priceless.
[1]: https://cs.wikipedia.org/wiki/Bo%C5%BEena_Kuklov%C3%A1-J%C3%...