There are several critical doping levels in the phase diagram of the cuprates where the ground state changes its nature. These are the levels where: antiferromangetisem is destroyed and replaced by a spin glass state, where superconductivity emerges, where the spin glass is destroyed, and, finally, where superconductivity is destroyed. These levels are not universal and the physical parameter that determines them is not clear. In this work we address this problem by studying the density of oxygen P_σ holes in the CuO₂ planes of the high temperature superconductor (Ca_xLa_1-x)(Ba_1.75-xLa_0.25+x)Cu₃O_y (CLBLCO) using the oxygen 17 nuclear quadrupole resonance parameter ν_Q. The two compounds we compare are of x=0.1 and 0.4 since they have a significant difference in the critical doping levels. We find that the efficiency of hole injection into the P_σ orbital in the CuO₂ planes is x dependent. In fact, the phase diagram is universal when using the P_σ hole density rather than the total oxygen level. This allows us to generate a unified phase diagram across the entire doping range, with no adjustable parameters, for the CLBLCO system even though the maximum T_c varies by 30%.