I thought the "Fancy" attribute was inherited, like with key lime pies. But key limes are marked as fancy ingredients, and Rockin' Wagons are not.
In this case, we had something we knew would happen some day: a non-fancy advanced cocktailcrafting recipe. If I remember correctly, we were betting this wouldn't happen, and internally all the AC recipes are assumed to be fancy.
I won't be able to play around with this for a while, but maybe Lost can take it into account in his concoction revamp?