I don't know how NASD decides on the dates, nor do I particularly care, although it would be interesting to know.
It could be in the NASD pdf file mentioned in your link, but it won't come up for me.
All that counts if NASD does set an X date is this, from your link.
"Ex-date or Ex-dividend date– On (or after) this date the security trades without its dividend. If you buy a dividend paying stock one day before the ex-dividend you will still get the dividend, but if you buy on the ex-dividend date, you won't get the dividend. Conversely, if you want to sell a stock and still receive a dividend that has been declared you need to sell on (or after) the ex-dividend day. The ex-date is the second business day before the date of record.
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