User blog comment:Xilinoc/Ch. 553 - Frozen Cross/@comment-10330822-20131016154408/@comment-1387259-20131017105400

That seems to be true for A (both A's) and B, but the rest are probably just epithets based on what they can do, and nothing more, not much different from how there's no actual ranking system to Arrancar numbered 11 and above.