Mine finally arrived (a while back, I admit) and I've now finally had time to examine them thoroughly.
The inlay area is nominally 1" and measures slightly smaller (0.990" to 0.995"), while the factory labels are slightly smaller again (0.987" to 0.992"). This tolerance is normal and expected, but IMO the factory labels are still a bit too big in some cases. I wouldn't cut them any bigger than 0.980".
In any case, anyone ordering labels from me doesn't have to worry about the exact super-precise size. Just tell me which chips you're labelling, Majestics in this case, and I will make them the right size.
For designing, aim at 0.980" and it will be fine.