Assembly Theory proposes that minimum joining count and observed abundance together quantify the selection required to produce an ensemble. We show that these endpoint measurements cannot identify whether joining was equiprobable or preferential. A finite joining process with equal pair probabilities and one with arbitrarily strong pair preference produce identical objects, copy numbers, assembly indices, and ensemble assembly with probability one. Equiprobable joining also attains unbounded ensemble assembly as the object and its required inventory grow. Assembly observables can therefore support an inference about selection only after a production model excludes such reconvergent processes.