These enamel dials, and the depth of the enamel, with my limited experience with the cloissone artisan with the Ulysse Nardin dials, can and will be different one from another even when made from the same artisan.
The hand appication alone has differences...hard to spot, but present none the less.
The baking and cooling environments are not always , in fact, not likely at all to be the same for each. The oven itself has different hot spots when I examine them, and the dials come out quite individual if you examine evry mm square of the surface...especially the refractive qualities of the translucent material.
This is the romance of enamel. Individuality.
However, with the possible event of industrialised making of larger numbers, this could even be more expensive, and less romantic...leading to the fact that these older ones will be more valued on the long run. Like the older Ming vases and ceramics of the past.