[tomatocracy]

> Imagine that the ex-date for a security is 2017-05-19. You sell one such security on 2017-05-18. Settlement clears on 2017-05-22. Because of the delay in settlement, you held the security on the ex-date (and on the day before the ex-date), but you're not entitled to the dividend because you sold the security before the ex-date.

That's right. The ex date is relevant to the day you trade (which in practice means entering into a contract to buy and sell securities at a certain price, not actually delivering those securities/money), whereas the record date is the equivalent for the day of ownership. The ex date will be X-1 business days before the record date with X and the definition of business day depending on the market settlement convention. In some markets X=1 hence the confusion between the two, I think.