Inhomogeneous substitutions (e.g. clustering and preferential site occupations) in compounds such as YBa2(Cu1-xMx)3Oy with M = Fe, Co, Ni, etc. are an unavoidable response to the changing redox environments in these O intercalation compounds. We collect here experimental evidence for various types of inhomogeneous distributions predicted on a thermodynamic model which considers the preferential "desorption" of O from various local environments. The parameter organizing the redox environment is DELTAH* (incremental enthalpy of oxygen desorption per mol O2). Theory suggests a sequence of discernible states represented by the acronym CLUSTER. With decreasing DELTAH*, indications for several of these states are obtained from Mossbauer and other experiments. These states are characteristically shifted in DELTAH* for different M. Also, further substitutions according to (YX)(BaZ)2(CuM)3Oy with X = Ca, Z = Sr, La can change the relevant DELTAH* for these states, allowing prediction of their preparation conditions. Aspects of the complex electronic phase diagram as a function of redox preparation are discussed.