There are many other examples. Topological spaces can be described as T0, T1, T2, etc. to indicate the separation axioms that hold on them. In part this reflects the tendency for there to be a first case that is degenerate or that common sense overlooks; for example, lines are one-dimensional and planes are two-dimensional, but mathematicians start with points, which are zero-dimensional.

It feels like this is related to the question of whether the "natural numbers" includes zero or not. In the set theory classes I took, we used N (in "blackboard bold") for the natural numbers 0, 1, 2, 3, ... and Z+ (in "blackboard bold") for the positive integers. My professor's pragmatic take on the controversy was that Z+ already means the positive integers, so it seemed like a waste to let N mean the same thing as Z+ and have no symbol to denote the nonnegative integers.