The difference between apprentice and master is akin to that of a surgeon, wielding either hacksaw or scalpel.
Outside of the army, the Nekrobiotek don't really distinguish themselves with ranks and titles to any great degree. There are the apprentice, who are not yet true Nekrobiotek and there are those who are. The master stands above them all, recognized by every Nekrobiotek as an outstanding scholar in the field of Necrology. They are the ones who have blazed a trail into unknown realms of science and wonder, stepping over corpses to do so in the most literal sense.
To be considered for the title of Master Nekrobiotek, the necromancer must have made some exceptional discovery or performed some great feat of wizardry. The title is most commonly given by the academy from which the Nekrobiotek came from or is associated with, though in the Abhimaan Monarchy
it is the royalty who bestow it. Such honors are granted rarely, even as research into the field continue at breakneck speed.
Among the Shinomas Magocracy, the rank carries even greater weight. The Master Nekrobiotek there command considerable political power and financial clout.
There are maybe a hundred or so masters still alive today. Each one has made significant and lasting contributions to Necrology and Necromancy, enough for their names to be well known far beyond their home nation. In more peaceful times, it was a great honor to host such a master and their lectures were crowded affairs. With the Long War, such visits have stopped and the master who remain have turned their considerable prowess towards finding new weapons to win the war.
One of the youngest and most recently recognized Master Nekrobioteks is Elaine Rae of the Korero-Take Republic, and one of the most controversial. While none argue her skill or power, the exact nature of the contribution that saw the senate elevate her to the rank of Master have been classified and remain secret even to some of the highest officials in the republic.