i insisted that people call my children by their full names.(benjamin and emily)
many people wanted to shorten Benjamin to benji or to benny. Now as an adult, my son most often goes by Benjamin, but some friends know him as ben. Its so much easier to make Benjamin into Ben. Once a childhood nickname is established, its very hard to change to the full name.
(my son has also taken to using his middle name--a name he disliked as child--as his cyber name.)

my family is filled with confusion because of names..
(there is Elizabeth, who was nick named annabel until WWII--when she picked up the name of "pidge' (short for pidgeon, her last name)--or my own mother -christened Nora Veronica, she is generally known to one and all as Vera--

and then there are the 'common names' that re-appear (call out Billy at a family reunion and up to 5 people could respond!)ditto for Jim/jimmy, or Tom/tommy or Dennis/dinny.

(i am a oner-what a surprize!--as are most of my siblings (my parents intentional effort)the only helen.)
(my sister geraldine 'shares her name' with a cousin-in-law)