I am trying to use Delta's system-wide upgrades on an itinerary from DTW to BOM via AMS. I purchased the appropriate M-class fare and tried to get on the waitlists for upgrade. Agent 1 could get me on the waitlist for AMS-BOM, but nothing else. She was surprised because they can usually override a closed waitlist for Diamond Elites. Agent 2 could do no better, but (after 40 minutes on the phone) tracked it down to the fact that the DL Revenue Department decided "to make waitlists unavailable in certain markets". Agent 3 managed to get me on a second waitlist (AMS-DTW), and got me listed as standby for Business on the DTW-AMS and BOM-AMS segments. Can anyone tell me the difference between being on the waitlist and being listed as standby for an upgrade?

Since the first 2 agents seemed befuddled (and I had never heard of it), I assume that the no-waitlist idea is a new one. I think it's a poor decision myself, but I'm not a DL bean counter. For me it just means that I'm less likely to pay the extra for M-class in the future.