Three different incommensurate phases predicted by the phenomenological theory of frustrated smectics were reportedly found in mixtures of DB8OCN and 8OBCAB and DB7OCN and 8OCB. The results of our high-resolution X-ray diffraction study of these materials show that these phases are, indeed, coexistences of two or more smectic-A phases. The correct phase diagrams of the two systems are found to be in excellent agreement with the phenomenological models. At this time, there remain no known materials that exhibit an incommensurate smectic-A phase.