"E"s in Overplus

This is the second time in a couple of weeks that I've seen E. Nesbit referred to as "E. E. Nesbit" (the first was in the Tom Shippey article I mentioned a few days ago). Where did the extra "E." come from? I'm no Nesbit expert, but as far as I'm aware she never published under that name, any more than Rosemary Sutcliff published as Rosemary Sutcliffe, despite popular belief to the contrary.

I suspect that in Nesbit's case, it's that we aren't used to writers having one rather than two initials: C. S. Lewis, J. K. Rowling, J. B. Priestley, E. F. Benson, H. G. Wells, etc: the pattern is two (or occasionally more, as with Tolkien), and Nesbit's missed beat makes us want to throw in another as a makeweight. The exception seems to be where the initial acknowledges an unfavoured first name, but only as the herald of the main forename, as in F. Scott Fitzgerald, but that's quite another kettle of rhythmic fish.