One of the issues I have come across with families paying some adherence to the naming pattern is that to avoid confusion, they seem to christen the child with one name and call him something else. With many records only having a first name on it, it is nearly impossible to know that the 'Maurice' on the records is in fact the 'James' you are looking for, as it is with one of my ancestors. Indeed, I have one family, mainly boys born in fairly quick succession, who only seem to be known by their second names. Thankfully, the 1901 census has the first and second names recorded- very helpful.
More common than you might think.
My nephew is officially one particular name but it has never been used.Instead he is known by an abbreviated version of a name that is not found at all in our family.This is used on everything he gets,despite having no official status.
A neighbour is the same,called a name that was something that his granny called him when he was young.
Strangely enough,my own godfather was unaware of what he was christened until he went looking for his baptismal cert. when he was getting married.He honestly got a shock when the priest told him that there was no one of that particular name on the register(Thomas *******) but there was a Martin ******* born to the correct parents about that time.
A bit off topic I know ,but have had many a "discussion" regarding both given and surname spelling and versions with people who try to tell you"but we never spelled it that way so it couldn't be our crowd"
For example people used Mcdonnell ,Mcdonell,Mdonnel,Macdonald,Mcdonald, etc as the same surname or Walsh,Walshe,Welsh,Welshe etc
Even simple versions of christian names can be different eg. Anne or Ann or Catherine,Katherine and Kate used on official papers plus lots of examples of people as the above poster mentioned,using their second name to distinguish themselves from another family member or even a cousin or neighbour(common enough where you have lots of different famikies in the same small area with the same surname