Hi, assuming you got your MECIR before july 2011 & then never renewed it again till last week, then yes you would have to give the Irex again. it has actually nothing to do with your NZ IR. Its just the way it is assuming you have not had any flight test between then and ur last week test. The problem is you let it expire for more than 12 months after the initial expiry. Your other exams given don't really count in this case. Also there are always other requirements to be done to keep urself legal between ur ratings being expired so have a read through. You could also try getting ur NZ IR renewed if you need it, but you might not be able to skip the IREX anyways.
The rules I have copied from CAO 40.2.1 given below. Alternatively you may download it from here
ComLaw: Legislative Instruments - Orders/Civil Aviation - by Title
its better to do what the Docs at Canberra say, than counter them. Its no use believe me.
Good Luck..Safe Flights
12 Renewal
12.1 A grade of instrument rating must be renewed for a period of 12 months from the date of its expiry if:
(a) its holder passes the instrument rating test applicable to the renewal of the grade of rating within the last 90 days before the grade of rating is due to expire; or
(b) its holder:
(i) is employed by, or working under an arrangement with, an operator who has a cyclic training and proficiency program that:
(A) meets the requirements of Appendix V; and
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(B) is approved under regulation 217; and
(ii) is a participant in the program; and
(iii) met the standards required by the program in the last session of the program that he or she attended.
12.2 Where an instrument rating has expired for a period of less than 12 months, an applicant may qualify for issue of a rating by passing the instrument rating test applicable to the renewal of a rating.
12.3 Where an instrument rating has expired for a period in excess of 12 months, an applicant may qualify for issue of a rating by passing the instrument rating test applicable to the initial issue of an instrument rating.
12.4 The holder is taken to meet the requirements of subparagraph 12.1 (a) if he or she complies with subsection 12A within the 90 days before the grade of rating is due to expire.
12.5 For paragraph 12.2, the applicant is taken to meet the requirements of subparagraph 12.1 (a) if he or she complies with subsection 12A within the period mentioned in paragraph 12.2.
12.6 For paragraph 12.3, subsection 12A does not apply.
12.7 To avoid doubt, for a person who is subject to competency checks by a training and checking organisation under subregulation 217 (2) of the Civil Aviation Regulations 1988 (CAR 1988), renewal of a grade of instrument rating using an instrument proficiency check on a flight simulator under subsection 12A may be conducted as part of the flight crew competency checking mentioned in subclause 3.4A of Appendix 2 of Civil Aviation Order 82.1.
Note For subsection 12.7 to apply, the respective requirements of subsection 12A and of subclause 3.4A of Appendix 2 of Civil Aviation Order 82.1 must all be met.