What I've found in the 'real world' is that most people have no idea
Sadie or
Sally are
Sarah nicknames. Absolutely none. The connection is lost. I think it's a similar thing with
Nancy and
Anne or
Polly from
Mary. Outside of the elderly who'd be more familiar with them, it only seems to be name nerds who are aware of it. That's just my experience though! My own grandmother didn't know her mother's name
Sally came from
Sarah originally.