Guidelines vs set Amount

[Missinformation]

I am a support payor. In 1998 my ex and I had a separation agreement (and subsequent divorce agreement based on same terms) that I was to pay an amount with a CPI increase annually. The FRO is now saying that I should not have paid the increase despite the agreement and I will be getting a credit.
My concern is that I have NOT been paying based on the guidelines but an amount set out between my ex and I. Can he go to court and ask for Retro adjustments based on my salary? If so, how far can he go back.
<OAlso, if I have had one of the children (there are 3 in total) for 7 years (and he has moved to another province about 8 years ago) would support, if he made more than me, be owed to me during that time?
<OMy 2<SUP>nd</SUP> child is almost done college (april 2013), my third is almost 18 and will be done highschool (without a diploma) in June 2013. I am almost done paying support basically.
<OMy biggest concern is that he can go back and ask for my financial records and ask for back support based on my income despite our agreement. I have another child with my current husband (who also pays support for one of his children right now as well)...this would cause great financial stress on us if I had to pay thousands of dollars in back support.
<OAny light you can shed on this would be helpful.

[OrleansLawyer]

Arrears in child support, particularly with a pre-existing agreement, is a complex topic in family law that brings together a number of important issues.

A parties' right to claim arrears in child support is extinguished when the child is no longer a child of the marriage, notwithstanding blameworthy conduct. If your children are almost adults then you are almost home free.

What is the difference between support you have been paying and the guideline amount? If the amount is nominal then you need not worry. If your income has increased significantly then a claim for arrears and higher child support become stronger.

There are a number of factors that contribute to the quanta of support arrears. Delay on the part of the recipient is addressed, as is blameworthy conduct on the part of the payor. The effect on the child, as well as the effect on the payor's second family. Some cases have held support changes from the date of filing. Notwithstanding exceptional circumstances, three years is an "absolute barrier" to most arrears claims.