A little more info that might help. Not sure when the 2 DC-9-31 were retired, but From Delta's DC-9 list and the current Parked list I have 2. Ship 9988 N8944E MSN
47176 was N3335L with delta back in the days, and Ship 9941 N3324L MSN47103 and was N3324L with Delta, Both were DC-9-30's, and both show show currently owned by Delta, and in storage.
If you like DC-9's, the storage list shows 8-DC-9-10's, 25 - DC-9-30's, 2-DC-9-40's and they are currently owned by Delta thru Northwest. The DC-9-50 are also all owned, and the number in storage are sadly going up untill the 34 are all retired. HTH.