Hmm, I think you're misquoting the article. Both the American city and the Prague alien city are part of the same "storyline" with the Hyperborea-start and Cairo before City 17 was thought up of. iirc they discarded the globe-trotting adventure plot so that the plot revolves around a single location, City 17 (which has always been based on Bulgaria, since it's established that the American city is actually Washington DC/Chicago for the previous storyline).
Speculation: The assets/levels that are already created for the world adventure storyline are repurposed for the City 17 storyline.
Hyperborea => Day 3 Borealis
Kraken Base => Day 3 Kraken Base
Vertigo => Day 4 Palace
Street War (the one with Merkavas) => Day 4 Street War
Cairo => Day 2 Wasteland
Prague alien city => Day 1 City 17
So this leaves Air Exchange and Ravenholm as something that are created after the worldwide plot is scrapped. Also, the Rooftops parts after Vertigo is very likely to be part of that earlier storyline as well since City 17's street war begins at the foot of the Palace after taking the lift down and there aren't any American skyscrapers anymore.