This is a first, in the sense that nobody in this forum has yet reported an unwillingness of A3 to honour the upgrade vouchers. Therefore my comments:

Considering that often business class consists of eight seats, four seats available for upgrade is also a first. Usually there are no more than two, and occasionally they'll free a few more around a day or two before the flight. As for the married segments, if one flies from HER (my home base) through ATH to an airport abroad, neither I nor any of my friends/family has ever been told that you have to upgrade both legs!

I can see a number of reasons why you got this obviously wrong info from them, and we'll know more once you answer Air Rarotonga's questions. Clearly, the first reason that comes to mind would be a new agent who's not been trained well-enough; HUACA would solve this.