If you remember, antartica, the second impact. just like the explosion in EOE. And then, the sea of Antartica was red. LCL red. My theory is, HIP had already occured before. And people came back with no rememberance of it.
I agree, it would also explain how and why the petrified headless-statue is around, and why Kaworu is ironically seated on top of it when he hooks up with Shinji for the first time, because it was a product of the previous Fall.
I've also been thinking that the SDDS are actually Adam's DNA itself, and that the way in which Seele can predict the evolution and arrival of the Angels is due to it being encoded into Adam's DNA, the SDDS would then literally be the instruction manual for life, that would contain the future destinies of all Angelic souls borne from it.