However, they are considered as a single unit, much like the 'll' or 'ch' have their own places in alphabetical order for Spanish, as if they were single letters

This was changed fifteen years ago (probably to make programmers happier). Now, officially, "ch" is sorted between "cg" and "ci" even if it is still considered a single letter and the same applies to "ll" (see http://en.wikipedia.org/wiki/Spanish_language#Writing_system).