The "Perpetual Union" ceased to exist the minute the ninth State ratified the Constitution -- by doing which, by the way, all nine of the ratifying States seceded, as admitted by James Madison in The Federalist, from the Perpetual Union.
By ratifying the one, they necessarily and ineluctably seceded from the other. Illegally, no less.
You will now concede this point and this argument, right now, forever, as a basis of further discussion. Give it up. Give it to me right now.
Actually no. They didn’t leave the union. Rather, changed the union. The Congress of the articles of Confederation made a resolution that the new constitution had been ratified, and the new government would take effect. The states never left the old union. The later joiners just weren’t in the new one yet.
As PeaRidge notes, the Federalist papers are of no constitutional import, and so Madison’s assertion that the states which ratified the Constitution had committed secession in them is of no value.
Or if you prefer, they retained their representation in the US under the A of C until the A of C transferred its authority to the new US of A under the current Constitution.
You lose either way.