Thanks, and I agree there is a possibility AZN might want to start a rolling BLA by releasing PFS before OS, even though they are coprimary endpoints.
A rolling BLA requires that each major section be submitted complete. So you can not submit some clinical data then roll in more clinical data.
The purpose of the rolling BLA is to get the "other stuff" reviewed started as you wait for trial results. Though investors focus on the pivitol data, submissions can, and are, CRL'd for both CMC and pre-clinical issues.
One can submit a BLA/NDA and later add data. So a sponsor could submit PFS hoping for an AA and then add in the OS data. But the PFS based submission has to be complete else the FDA will refuse to file it.