Does it reference that in relationship to adult adoption?
You think that matters why? Many states do not differentiate between an adult adoption and a minor adoption. In fact some of the states where there is no difference even require a home study be performed to ensure the adoption is in the best interest of "the child".
My simple point is making a blanket statement that no state allows an adoption where one of the existing legal parents retains their legal relationship with the adoptee when the second parent is not a spouse of the parent retaining their legal status is incorrect. Second parent adoptions have been allowed in some states. Many attorneys will provide the blanket "no state allows second parent adoptions" because they are not aware some states do. In fact, in perusing the web I have seen q and a sites where attorneys from states that have allowed second parent adoptions have responded with a resounding; nope, not happening. Law is a living and evolving entity. If they don't practice in areas of the law involving second parent adoptions and associated areas of law (it involves the lgbt- whatever community a lot), they simply may not be aware of the changes taking place.
I asked the state involved because it does make a difference (just as it does in almost every question posed here) It wasn't out of enjoyment of punching a keyboard. The state(s) involved does make a difference and as much as I enjoy researching, I'm not going to research 50 states for such a question.