I have discovered three instances of miles disappearing from two separate Delta accounts (one household), all in the month of Jan 2008.

The small one is an unexplained 1628-mile deduction that was logged on Jan 29 2008. The amount matches a 1628-mile credit legitimately earned on Continental the same day. I didn't notice the deduction until last month; when I called Delta to get the miles reinstated I was told it's too old and their records don't go back that far. I figured it wasn't worth arguing about, but then another as-yet unexplained disappearance happened, and involving a lot more miles.

In Oct 2007 my partner and I cashed in 180,000 miles for two BizElite tickets to Europe (the good old days). On the outbound trans-Atlantic segment there was an last-minute aircraft change on the same day that new BizElite inflight service rolled out. Long story short: we got lousy seats and food and drink was not served until halfway to LHR (the food was cold, the white wine was warm -- ack!). I wrote to Delta and asked for 15,000-mile credit for each of us; on Jan 4 2008 they wrote back and said they would issue a credit (though didn't say amount; I have the letter). When I checked on-line, each of us had been credited with 10,000 miles, which I felt was fair.

Now I look at my statement (which, since the end of mailed statements, I have only been printing on Dec 31 for the 12 months previous) and I see the 10,000-mile credit has disappeared from both our accounts.

I will definitely take this up with Delta, but has anyone else had similar problems (especially during Jan 2008) and can you provide hints for a successful resolution? Yes, I realize I should be auditing my statements more than annually, but I honestly didn't think Delta's system would slip up this badly!

UPDATE: I went ahead and did something I've never had to do with any mileage accounts -- I added up all the miles shown on my statement to see if the total matched at the end of the year. For 2008, in both accounts, it didn't.

Neither of the 10,000-mile credits appear in our printed statements for the 12 months ending 12/31/08, but when I add up all the miles shown on the statement for the 12 months, it comes up 10,000 miles short of the total appearing at the end of the year. The Continental miles that were mysteriously posted and then deducted appear in the total. And everything tracks forward to today -- nothing missing from the total.

All very strange, but it appears I wasn't shortchanged by the Jan 2008 glitch.

I do remember several years ago where they just deleted several entries instead of posting corrections on my account. They were correct in making the adjustments (miles posted in error), but I was surprised that they would do it by just making the whole thing disappear.

On your 10,000 mile credit, could that have been posted as MQMs? Those don't show in your skymiles balance.

BTW, I check my account online monthly, if not weekly. My business partner had 100k miles deducted from her account a couple of years ago. She called and they told her someone had cashed them in for tickets (obviously not her) and it took quite a while to get them to reverse it. Never did find out if it was a DL mistake or someone got hold of her account number & password.