A Polish carrier would probably be built abroad and survive 1939

What difference would a Polish fleet carrier ready around 1939 make?

Built in Britain or America, it could survive the invasion and might also draw additional Polish escorts safely into Allied service.

Poland lacked the domestic slipway capacity for such a project, so a carrier would likely be ordered from Britain or possibly the United States. If completion approached in 1939 or 1940, the hull might still be in a foreign yard when Germany invaded and would therefore escape capture. Polish destroyers or other ships sent to escort the carrier home could also remain outside the Baltic and join the Allied fleet. Funding might rely on public subscription or foreign credit, making the idea a force-building and industrial counterfactual rather than simply the unexplained appearance of another flight deck.