Every state is different so you'll have to check with your state Agriculture Dept.
Here for example, we don't need NPIP at all for anything unless we're trucking chicks into the state or showing chickens in poultry shows.
I went into our post office and asked them what happens if I order hatching eggs from someone that is or is not compliant with NPIP, or vice versa. I was told that the USPS doesn't care what certifications anyone has for shipping anything.
And that makes sense. So, who's really checking any of this?
I believe it's more meant like our state does it...if you're going to mass ship chicks into our state, or you want to bring your chicken to a poultry show, then you'd need to be NPIP. I personally don't care if they are NPIP as that doesn't tell me they've been checked for MS, AI, or Mareks.