If you check the online newspapers in the UK and overseas you will find reports quite often on prisoners where they were sent what area of the country and to whom.(Although I have not as yet unfortunately found a criminal in my personal ancestry,being Border Reivers I suppose they all were.) I have noticed in other family members plenty of all ages and sex. No doubt your ancestors,if they wanted to maintain contact with a family member they just wrote c/o of the Post Office of the capital city in that area. Up until 1960 a letter would reach our family with just my grandmothers name and New Zealand (she was an avid letter writer) . I recall one letter that the person had just put her name and Levin and no country one that I suspected must have traveled the globe as two years later it came back to us,with try Ireland written on it, then another note send to New Zealand.
It appears in those days rather than just sending mail back to where it came from if you are lucky, the post office tried to get it to its destination. Unlike these days when if you put an address on the back and it doesn't get delivered, only because the stamp forgotten,has fallen off or is insufficient postage, size,shape, weight wrong, you have to make a trip to the post office to discover why and pay again of course. Undelivered Christmas cards are not returned, so unless you follow up with a letter to a card someone could be dead and you wouldn't even know.