The most common example is actually scandinavian unbabtised babies. It's quite common to keep the name secret until the big reveal in the church when the child is several months old. I believe that here in denmark you aren't required by law to submit a name until the child is 6 months old.
you can go past 6 months without naming your child but you are fined, I can't remember at which point the child will be given a name if you won't provide one.
Also of course if you give your child a name that is not recognized as a name by the name register there is a process for okaying that name, so in that case your child can have a name in the family but not an official governmental name yet.
