In our long-term follow-up studies we only expect Investigators to review Six-monthly Safety Reports, not individual SUSARs. Fortunately the regulations are vague enough to not specify the exact format of how Investigators should receive SUSARs (or when), so as long as you agree & define your own process in your own SOP and you follow it, I don't believe it matters how you send the SUSARs (either individually or in SSRs).