Sankey diagram illustrating formation channels of WR–COs that are also BCO progenitors. We show our fiducial sets, simulated assuming a delayed CCSN model, G20 natal kick model, and α_CE = 3; for solar (Z = 0.02, left) and sub-solar (Z = 0.00014, right) metallicity. We distinguish “direct” WR–COs from “indirect” WR-COs. “Direct” WR–COs are produced by a WR-WR post-CE binary; “indirect” WR–COs avoid the WR-WR evolution. Unlike “direct” WR–COs, WR progenitors in “indirect” WR–COs have the possibilty to start a stable mass transfer (indicated with SMT) or a CE phase between the first CO formation and the WR–CO phase. Few "indirect" systems avoid further mass transfer (indicated with MT) episodes.