Official was probably a bad word to use since it has 'legal' type connotations in some peoples' minds.
What I meant was that, if you ask someone to list the nicknames for, say, Elizabeth, or William, or Katherine, there are a distinct set of nicknames that are recognised as belonging to those names. Less well-known names like Jocelyn don't necessarily have that distinct and instantly recogniseable nickname set. If you're introduced to someone named Liz, you automatically assume that their full name is Elizabeth. But if you're introduced to someone named Joss, you may wonder whether their full name is Jocelyn or Josephine or something else, or if it's just plain Joss.
So, "official" in the sense of "universally accepted and recognised", not in terms of "enforced by statutory authorities"!
♦ Chrisell ♦
All we have to decide is what to do with the time that is given us. - J.R.R. Tolkien.