The Conway-Wechsler System is a system for naming numbers, with the goal of being largely consistient with the way numbers are named in English, but having no upper bound.
The basic idea is that "XilliYilliZillion" denotes $10^{3(100000X + 1000Y + Z)+3}$, where X, Y, and Z are represented in English via Latin prefixed. So $10^{3(1000003)+3}$ would be "1illi0illi3illion", which with the numbers replaced with Latin prefixed is "Millinillitrillion". This "zillions" can be combined with the names of lower numbers to represent any natural number in English.
I am confused though. It appears that the larger latin prefix they list is for 999, so the largest zillion should be "nongentinonagintanovillinongentinonagintanovillinongentinonagintanovill" = $10^{3(999999999)+3}$.
I think I'm having trouble understanding the rules of the Conway-Wechsler system. What I am missing?
maybe I don't understand your question, but "XilliYilliZilliWillion" would denote $10^{3(100000000X + 1000000Y + 1000Z + W)+3}$, and so on: you have just to add some other -illi-s to extend the number system indefinitely.