The Wikipedia article on naked short selling says
It is difficult to measure how often naked short selling occurs. Fails to deliver are not necessarily indicative of naked shorting, and can result from both "long" transactions (stock purchases) and short sales. Naked shorting can be invisible in a liquid market, as long as the short sale is eventually delivered to the buyer.
My understanding is that with normal short-selling, the share is delivered immediately. Whereas with naked short selling, the share cannot be delivered until the short-seller repurchases it.
So my question is, why doesn't this difference in timing of delivery reveal whether a short sale is naked or not? Similarly, if you take the other side of a short sale, how could you tell whether it's naked?
I'm most interested in the U.S. stock market. I hope the question is not too applied for this site.