Median fractions f_from of BCOs with WR–CO progenitors as a function of metallicity Z and common envelope efficiency α_CE. Left (right) plot shows the α_CE = 1 (α_CE = 3) case. We distinguish fractions f_from of BBHs evolved as WR–BHs (purple dotted lines, plus sign markers), BNSs evolved as WR–NSs (orange dashed lines, cross sign markers), BHNSs evolved as either WR–NSs or WR–BHs (blue dash-dotted lines, hexagon markers). We also show the fraction of all BCOs with a WR–CO progenitor (black lines, round markers). For each (Z, α_CE) pair and BCO type, we consider the distribution of the 12 f_from fractions of the correspondent simulated sets (combinations of CCSN and natal kick models, see Table 1), and we show their median values (scatter points) and 68% credible intervals (error bars).