I have the Attorney Generals office on the phone and they told me that they do a review every three years, and that I'm the only one that has to supply proof of income.
Either parent can go to court when circumstances change and request a modification. If you are in court, you can serve discovery requests upon the other party and insist that they provide proof of income and expenses. The three year review should be a complete review, based on the income of both parents. The official published information all states that the review is done at the request of the custodial parent, not automatically. That doesn't mean that they cannot do it on their own initiative.
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