In my view, this may be the single most irritating thing about Delta. They offer these promotions by the hundreds, while having no capability of fulfilling them at the time they are offered -- if ever! They make you check a million times, re-register, speak to a dozen idiots who ask you to chase your tail, etc., etc.
I know that this sounds stupid (because I like miles as much as anyone), but Delta would actually provide BETTER customer service if they simply stopped offering these promotions. Don't offer something that you aren't prepared to deliver. It results in bad customer relationships and makes you look incompetent (which may be the truth -- at least in this narrow area)!
Bruce