after ECB's realized gains are booked to PnL, the ECB splits up the net profit as: ➖ up to 20% to the general reserve fund, which can be used to offset future PnL losses ➖ the rest distributed to the NCB's, proportional to the National Central Bank's paid-up shares
thus, unrealized gold gains accumulate on the ECB's liability side, under the revaluation account, and the only way they can be debited (e.g. to cover expenses, or credit an NCB's reserve account) is: 1️⃣ when the ECB sells the gold, thus turning an unrealized gain into a realized one 2️⃣ offset future losses in the gold bucket