I found the reference in CAA NZ Part 61:
61.37 Recent flight experience
...
(i) If the holder of a pilot licence issued in accordance with this Part has
not met the requirements of rule 61.39 for a period of 5 years or more, the
privileges of that pilot licence may not be exercised again unless,—
(1) the holder of the pilot licence passes an approved air law
examination and meets the appropriate currency requirements of
the licence (except if the holder has a current pilot licence for a
different category of aircraft and meets the requirements of rule
61.39(a) for that category); or
(2) in the case of an airline transport pilot licence, the holder of the
pilot licence completes the appropriate operational competency
checks required in Parts 121, 125, or 135 whichever is
applicable.
where 61.39 is:
61.39 Biennial flight review
(a) Except as provided in paragraph (b), the holder of a pilot licence
issued by the Director under the Act and this Part must not exercise the
privileges of the pilot licence for longer than 24 months from the date of the
issue flight test for the pilot licence unless the holder—
Civil Aviation Rules CAA Consolidation
10 March 2017 31 CAA of NZ
(1) has successfully completed a biennial flight review under
paragraph (c) within the previous 24 months; or
(2) for a glider pilot licence, has successfully completed a biennial
flight review conducted by a gliding organisation within the
previous 24 months.
....
(plus plenty more)
Note that the law exam must be the one for your licence type - PPL/CPL/etc.
I think you could interpret this as 5 years since your BFR expiry (therefore 7 years since your last BFR date of issue). But if you're in that grey area you should probably contact the CAA and get them to confirm.