Personally I don't think there is anything wrong with the Jet Age/DOTM/Modern Times/Fly to the Future names for shorter games and just appending that to the "Gameworld (Insert famous name here)" works.
Another thought is to take the create 3 categories of short, medium and advanced length, along with a 3 part bar coloured green, yellow and red. The coloured bar acts as an easy way to see the length of a world in a more generic way, without resorting to calling a world Long or Short of whatever. Along with this, a descriptor of the challenges faced in each.
Short - Short Length Gameworld where long term fleet planning is not necessary.
Medium - Medium Length Gameworld where spanning two generations of commercial aircraft, where fleet changes will likely be necessary.
Advanced - Long Length Gameworld which spans multiple generations of commerical aircraft, long term fleet planning and multiple fleet changes will be necessary in this gameworld.
Something a bit like that, although descriptions might be in need of a little work. Beginners World, I would keep calling Beginners World, rather than Gameworld.
With the longer Gameworlds, you could say they are in need of their own name, rather than changing over time, I like "Airline Generations" although, "The Age of Flight," something that signifies the length of time covered without getting a specific as the others.
So a new longer gameworld, could be "Gameworld Amelia - Airline Generations" with a full Red bar signifying the world is of advanced length, along with a description, probably in the "See Details" section, of what that means.
A Short one would be "Gameworld Amelia - Jet Age" for something covering 1955-1976 with a 2/3 yellow bar signifying world is of Medium length, again, along with a description.