It's easy. You just save them on your phone as
(Hannah who works down the florist's)
Hannah Flowers
(Hannah that I met at a party and all I can remember is she's from France)
Hannah French
(Hannah who I know through her mum Julie)
Hannah Julie'sdaughter
(Hannah who's a brunette)
Hannah Brown
Even easier if everyone else uses the same shorthand to distinguish one Hannah from another too. Then I guess if she has kids they could use the same distinguisher, just for the sake of simplicity and so people know they're related.
So still surnames? Just ones you've made up. And if Hannah Flowers gets a new job or Hannah Brown dyes her hair, then what?,
*And you couldn't talk to anyone else about them. "Oh do you know Hannah Flowers", "No", "I'm sure you do, she works at the florist", "oh you mean Hannah Neighbours, she lives up the road from me"