We're still waiting, waiting, waiting from NVC/Joberg. Our NOA2 came the first week of March, so I'm just trying to relax and let them get around to it. At the end of March, I got our NVC case number and just status check from time to time.
I'm not sure how thorough Zambia is, but Joberg just pushes packets 3 & 4 at the beneficiary's email in one fell swoop. Or so I've heard. Hopefully you're on track for your interview now!