I too find this interchangeability, even apparent adoption of or being brought up by names completely removed from the given, birth name a real PITA at times.
 Lady on the left? Mary Elizabeth. aka " Polly ". Don't ask me how they managed That one!
 Uncle Fred was born Thomas. Uncle Bill was Roy. Uncle George still is Frederick, though I can't imagine he'd even turn round if ye called him Fred! Aunty Pip? God knows! I could go on and on.
Why? Why call a kid William, on his birth certificate, then call him Jacob, to his face for the rest of his life? I seriously wonder if half of them even knew their real names.
 Oh and Danuslave / Linda; Yeppers. Frank / Francis. I too have even just recently fallen foul of that one!  
