The NTZ is laterally limited by the adjacent normal operating zones. NOZs and NTZ do not overlap.
The wording "located centrally between the two extended runway centre lines" is a bit misleading. The NTZ is between the centre lines, but it is not limited by them.
In other words, the width of the NTZ is defined by the width of the NOZs (see 1.2.2.1.3 of PANS-OPS Volume I, Part III, Section 2).