I tried pricing award tickets from PHL to SYD. Kept getting message: " We're sorry, SHIB. No results were found for your search. Try changing your cities or dates. Some itineraries may not be offered on delta.com. Please call the SkyMiles Diamond Medallion line at 877-220-6888 to see if your flight is available."
Tried originating at BWI... same "not available" message.
Tried both PHL and BWI for various periods, as far out as the system would permit. No luck.
Plenty of itineraries offered for $$$ but none for miles.
Found award tickets originating in ATL.
And, yes, I was logged in to my account.
Called SMS and the agent was seeing the same problem when he tried an internet search. He was able to find award tickets from within DL's internal system.

