As a twin, I got used to being called the wrong name. Part of the territory. It stopped happening after '01, when I got married, moved 40 miles north, and began collecting a different set of friends acquaintances, in-laws, and co-workers. However, I still joke "Steve or Steven, just don't call me late for dinner."
When my twin was a toddler, my mother decided she didn't like his birth name, and so de facto changed his name to Tristan. By the time I was old enough to care, just about everyone called him Tristan (I think one of the aunts would occasionally call him Robert.) This lasted until we started going to college. Something about college forms being sticklers for legal names. And so, Mom sat us down and told us that when we went to college, he would be Robert, sharing a name with my dad's brother who died too soon. So, outside of Leavenworth, he was Robert. At the community college. At Western. Honestly, by the time we started at Western 3 years later, only folks from the church and the occasional throwback at home would call him Tristan. He's on my phone as Robert, and when I e-mail him, I type "RJ" - the first letters of his e-mail address and his first and middle initial.
Every year, we have the school musical. (Two of them, actually, the winter and the spring.) And, after the first time, it's a ritual. Collect the program, and see if Molly is listed as Molly Pratt, Molly (birth name), or Molly (birth name misspelled). So far, it's been a random draw on it.