Hmm actually the connection between Boris and Sergei makes me wonder, why didn't Orth-Meyer order a hit on Sergei when he did Fabian? That is assuming the Bjarkhov Bomb takes place during C47, which I'm almost certain it does.
Orth-Meyer seemed to be going after not only the other 5 fathers but also people related to them. Did Orth-Meyer just not know about Sergei? He's not exactly a low profile person.
Edit: To avoid triple posting like a freak I'll just leave this as an edit:
You've been noticed by senpai, Agent4T7