I’ve been (very slowly) building up NP3. Had assembled fork to figure where to cut the steerer tube. When I removed the fork to make the cut, the lower headset race came out one piece at a time (see pic). I thought this was supposed to be a sealed bearing? Is it supposed to come apart like this? It’s never been ridden–so no use at all. Can I just fit it back together and continue? I wanted to get the cabling done today.
I think the NP3 uses standard 36x45 sealed bearings from Cane Creek. These can come apart fairly easy if one of the races is stuck in the headtube or on the steerer. Your bearing retainer looks undamaged and none of the balls are missing so you should be able to just reassemble it.
On loose ball headsets, bin the cage and put as many loose balls in as possible and then remove one.
Stick them in place with grease during assembly.
It will make for a smoother longer lasting headset that won’t get the tendency to steer like its on a ratchet in later life.
I have a early XTR headset set up this way and it is still buttery smooth, dare I say indistinguishable from a brand new ‘king’.
WD 
SummitAK is correct. This is a sealed bearing. I just pressed the other half back in and moved on. Seems to work smoothly.