  The critical doping levels in cuprates, where the ground state changes its
nature (from an antiferromagnet to a spin glass to superconductor to metal),
are not universal. We investigate the origin of these critical doping
variations by measuring the in-plane oxygen $p_{\sigma}$ hole density in the
CuO$_{2}$ layers as a function of the oxygen density $y$ in (Ca$_{x}$
La$_{1-x}$)(Ba$_{1.75-x}$La$_{0.25+x}$)Cu$_{3}$O$_{y}$. This is done using the
oxygen 17 nuclear quadrupole resonance parameter $\nu_{Q}$. We compare
compounds with $x=0.1$ and 0.4 which have significant critical $y$ variations
and find that these variations can be explained by a change in the efficiency
of hole injection into the $p_{\sigma}$ orbital. This allows us to generate a
unified phase diagram for the CLBLCO system across the entire doping range,
with no adjustable parameters.
