Good call SpiritWind!
I found L2, K2, Z18, and Z19.
I still have quite a few plots to open, so I went back and checked all of them I could.
So It is a discount but not half off. For example, Z18 is 9 lanterns instead of 11 and 6 permits instead of 8.
When I opened Z19, Z20 was not on sale.