There is a process. Previously, the bookcases on the right (lower 4 shelves) of the picture held my trade1st editions in alphabetical order, aside from the DT series leading off. When a new noverl came out, shifting was required. Contemplating, but, unlikely, organizing them by publication date, that way stuff is added at the end.
Either way, the book collector rule/axiom is that empty shelves are soon filled.