Among the thirty Aethyrs, the tenth, ZAX, is structurally unlike any of the others, and the fact can be verified by anyone willing to count letters.
Dee's system centres on the Great Table, a grid of letters divided into four elemental Watchtowers by a cross of single-width arms running through it. That cross is called the Cross of Union or the Black Cross, and from it are drawn four names: EXARP, HCOMA, NANTA and BITOM, associated respectively with air, water, earth and fire. Together they form what later practice calls the Tablet of Union, the element that binds the other four together.
The three Parts of ZAX are Lexarph, Comanan and Tabitom. Written out in sequence they give LEXARPHCOMANANTABITOM. Set the initial L aside and the remaining twenty letters divide exactly, and without remainder or rearrangement, into EXARP, HCOMA, NANTA and BITOM.
This is not an interpretive claim. It is an arithmetic property of the names as they stand in the manuscripts, and it is the single strongest piece of internal evidence that the Enochian material was constructed to a plan rather than improvised session by session. Whether the plan was angelic, Kelley's or the product of some process neither man understood is exactly the question that the record does not answer, but the plan is undeniably there.
Nothing in the received text draws attention to the pattern or explains why the names of the binding cross should be distributed across a single Aethyr's three Parts. It was noticed later, and it has shaped how ZAX is treated ever since.