What designer bag does not lose value?

I'm curious, when it comes to the world of designer bags, is there truly a brand or a specific model that consistently maintains its value over time, defying the usual trends of depreciation? In a market where luxury handbags can often see significant fluctuations in their resale prices, I'm wondering if there exists an exception to the rule. Is there a designer bag that, much like a fine investment, not only retains its charm but also its monetary worth, proving to be a smart addition to any collector's portfolio?