And also, I saw this article on a lawyer's website (David A. Zuckerman), which is EXACTLY their case, but I think is not accurate because I then read somewhere else that priority date retention only applies to category F2, not F1-4.. So I suppose the following would be inaccurate?:
"Another provision of the CSPA applies in cases where a child is over 21 and the wait for a green card took a very long time. The law states that if a child was under 21 when a petition was filed, but is now over 21 by the time the green card was issued, the child can retain the priority date of the original green card petition in a subsequent petition filed by the child’s parent. If the old priority date is far enough in the past, then the child’s priority date becomes current, and a green card becomes immediately available to the child.
For example, let’s assume that a U.S. citizen files a petition for his brother’s family back in 1984. The brother has a wife and two children, who were ages 4 and 5 when the petition was filed. Twenty-three years later, in 2007, the brother and wife get their green cards, but the two children, now ages 27 and 28, have “aged out” and must stay behind in the Philippines.
Now that the brother has a green card, he can file petitions for his two children, but it could take 10 years or more for their priority dates to become current. Under the CSPA, the children’s priority dates can be backdated to 1984, which is earlier than the current priority date of October 1, 1996. This makes the children immediately eligible for green cards."