Most of the complexity of the stories has developed as the...

Most of the complexity of the stories has developed as the stories came along (and may be a product of the principle that "nothing is what it seems"). I did start with some essential ambiguousness in the aliens' motivation and the questions this raises in human minds, which I consider to have been disregarded in Contact (novel and film). That, in part, may be what has delayed the writing of the fifth and sixth novelettes in the series.