The 2002 CSPA law is always challenged by the USCIS when it is brought to bear on immigrant petitions filed before 2002. One of the legal arguments is that CSPA doesn't retrospectively benefit earlier immigrant petitions because that would be unconstitutional under the ex post facto clause of Article I, Section 9 of the Constitution.
Consequently, the immigration matter has to be decided by Federal Courts which usually end up benefiting the immigrant. The Courts revert back to Justice Chase's decision in Calder v. Bull case of 1798, where he outlined four classes of laws that are unconstitutional on the grounds of ex post facto.
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I am not an immigration attorney nor do I have any experience litigating immigration cases. As always, seek professional advice before pursuing any course of action. I cannot be held accountable for any consequences of my comments.