The Case of the Missing Lands

Glass coaster set

This set of coasters is one of the most popular* early Walt Disney World souvenirs.  Four of the Lands of the Magic Kingdom are featured on these tiny 3 1/4" glass coasters.  Why only four?  Why no love for Frontierland or Tomorrowland?

The coasters match the design of the also popular* ruffled bowl.  The bowl, with 6 spaces for images, also leaves out Frontier and Tomorrow.  While only artist's renderings, can you spot the errors in Adventureland & Liberty Square?
*based on frequency of appearances on eBay