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!