In the opening stage, are there any moves that are perfectly sound but are not book moves? Here a book move, is defined in Wikipedia as follows:
Opening moves that are considered standard (often catalogued in a reference work such as the Encyclopaedia of Chess Openings) are referred to as "book moves", or simply "book". Reference works often present move sequences in simple algebraic notation, opening trees, or theory tables.
By a sound move, I mean a move that is completely reasonable in a certain opening position and does not create any weaknesses. (There may be a better definition, but you probably know what I mean.)