HJ, are you referring to long sweep 90s on a horizontal drain line? I'm not sure if my county allows those (we have lots of dumb extra rules), but those I think are fine. I was talking about the tighter elbow, i think usually you guys refer to them as vent elbows. Sorry if I wasn't clear on that, I usually just call that a 90 and the other a long sweep 90.
I was told by local plumbers that we can't even use the long sweeps on their side in my county. As dumb as it is, we had to do a 45 and a street 45 to make a 90 turn, which is exactly the same thing, but has an extra potential leak point. yeah... dumb.
Looks like you have quite the mess of a project there now... Def want to get some kind of venting on that, even if you have to just do a couple AAVs (as a last resort). You might have a vent in there somewhere you can use, but its hard to tell (for me at least) from the pictures. The Line B... is there a kitchen sink, shower, tub, anything near there? Could this be a trap vent for a floor drain? Plumbers, can this be used if it is a floor drain vent, or would that overload it?