Delta Asia award prices fluctuate - is there even a System?

Booked intra-China one-way award for 17500 miles (120 days out). Y award was 15k miles.

But Delta award chart lists 30k (J), 17.5k (Y) miles - what's going on?

Must say - Delta website is much better - fewer steps, save confirmation in pdf - you can tell it's a more well-run operation.......

........all the better to squeeze Delta frequent flyers