The Vacheron Constantin Overseas Perpetual Calendar Ultra-Thin Skeleton Ref. 4307V/220G-236C is an exceptionally high-end Overseas model combining an openworked perpetual-calendar movement with an 18K white-gold case and sapphire bezel. The exact reference you provided appears in a current 2026 marketplace listing; Vacheron Constantin's official catalogue also confirms the Overseas Perpetual Calendar Ultra-Thin Skeleton family in 41.5 mm white gold.