What's in a name?

Okay, not only were most of the Irish records burnt, middle of the nineteenth century, and the spelling not-standardised, but written in Latin (sometimes). e.g The Latin “J” was written “I” regardless of grammatical changes in names, little things such as Ioannes and Johannes being John are not too easily seen.
Parish records were either written in English or Latin. Never in Irish. The surname ALWAYS retains the English spelling (or a phonetic variation – the same surname can be spelled differently in any set of records, probably depending on the way that the person writing it spelled the name, and whether that person was a local to the area or not.) The rules of Latin are not necessarily followed, the spelling of the name changes and does not become what it should become. That is to say, Latin has rules and with those rules the basic name will change indicating a parent or a child. The child’s name will be given in it’s basic form – that is the nominative form, but the end of the parents name will change somewhat (the genative form). Putting this as simply as possible, the child may be called after one of the parents, but the spelling of each name while it looks almost the same will end differently.
So, I wonder ,what is the Latin search for Mary Jane? Maria = Mary, Maureen, Molly, Marie. Jane = Joanna, Johanna, Joan, Jeanne, Jeanette, Joanne, Sinead, Siobhan, Jean and Honora.
Was Mary Jane being mysterious or had she mystery thrust upon her?