No

Is shards of atheria book 7 of 8BW

No

What is it then

SoA is a non-canon prequel to 8bw books

That said, you should still read it as it may help you understand aetheria better, although again, it is not canon, so not everything inside it can be stated as fact

I know.

However, it's our only pre-crash source.

Not really. Its non canon, so the only confirmed pre-crash data is that there was a nuclear war