Population and elevation are later additions. (Although later does not necessarily mean inferior)
Replacing both for 'established 1971' is what
@lazyboy97o always calls Disney becoming ever more self-referential. The sign does not tell you anymore that you are in Main Street, America, but in Disney Parks.
It is in line with a Skipper Canteen, which replaces actual tropical setting for the Disney tropical ride setting. Related to how Fantasyland is no longer an imaginary random European town that sort of is the origin and setting of many of Disney's fairytales, but the Disney fairytales world itself ('worlds themselves', plural, to be more precise). Main Street for its part, like the Rivers of America district, slowly replaces the Americana for the Disneyana.