The magnetic irreversibility-field lines (Hirr(T)) for both non-substituted (x = 0) and Ca-substituted (x = 0.1) Cu2Ba2(Y1-xCax)Cu2O8±δ superconductors of the Cu-2212 structure (so-called `124') with a Cu2O2±δ double chain as the charge-reservoir constituent have been established. The obtained Hirr(T) lines are compared to data measured for CuBa2(Y1-xCax)Cu2O7-δ samples of the Cu-1212 structure (so-called `123') with a CuO1-δ single-chain charge reservoir. The Ca-free Cu-2212 sample with Tc = 80 K is assumed to be underdoped in terms of the hole-doping level. Increasing the hole-doping level through the Ca(II)-for-Y(III) substitution not only increases the value of Tc, but also shifts the Hirr line towards the higher magnetic field regime. Nevertheless, the Hirr(T) line for the Ca-substituted Cu-2212 sample (Tc = 87 K) is clearly located lower than that for the Ca-free sample, which is of the optimally-doped Cu-1212 (Tc = 91 K) phase. This is attributed to the yet higher overall hole-doping level of the Cu-1212-phase sample. It is interesting to note that for the Cu-1212 phase, the Hirr lines are nearly identical for both the Ca-free and the Ca-substituted samples, even though the Tc decreases with Ca substitution. This is believed to be due to a slightly lower oxygen content in the Ca-substituted Cu-1212 sample.