I've seen a cartridge headset at velo orange with a split crown race. (see here)
From what I read in the comments, I realized it's technically not a race since the bearings roll within the cartridge.
I then guess that the race (Chris King calls it a base plate) is more or less secure on the crown and could move a bit on the crown. I'm wondering if it's ok to have a loose race on a cartridge headset, say like a spacer between the stem and the upper cup.