Theories about Ricken's odd friends/devotees
(An aside, I'm not sure that now all existing sessions of the series are concluded whether or not we're supposed to apply "spoiler" tags. Let me know)
So Rebeck and Patton are on the outer edge of the people oMark is acquainted with, he knows them via Ricken.
From Rebeck's complaints about being pecked by birds on the back of her head to Patton's general strangeness and the way they interact, it seems like they may have been subject to some sort of Lumon's experiments. It doesn't seem like they'd have been severed but it really isn't clear what happens after a severed employee is let go. Burt seems to be fine for the most part, for example.
So why are they weird? I'm thinking it was some early prototype of the Severance procedure. Not enough to create the innie, but enough to prove key aspects of the technology. Also, they may have been a part of this at a fairly young age.