Sorry, but I should have said something about the "degree"
or "level" of an NBX. Numerical series of the form n-m-n
(where m is 0 if no midpoint) I would refer to as '1st degree',
and so on on up in complexity. First-degree NBX's can
easily happen randomly, and are thus so common as to be
unremarkable. But as the degree of an NBX increases, the
chances of its occurring randomly is geometically decreased,
so that even a 3rd-degree NBX must be relatively rare.
Furthermore, even within the same level of NBX, the cases
where the non-middle terms form a steadily-increasing or
steadily-decreasing series of numbers are particularly suspect
of intentionality, provided that they occur in a portion of text
that is otherwise important on its own account. Such is the
case of the Prologue of Coptic Thomas, where we have
a 3rd-degree NBX whose terms are steadily-decreasing,
in the form < n, n-1, n-2, 3, n-2, n-1, n >, where n=11. Note
that if the mid-point had not been a 3-letter word, it would
not have been possible to divide the whole as was done,
nor would such a thing have been possible if the outer
terms had been other than they were.

Mike G.