I was thinking about this question when I saw 6 stories in a row for the same city. I opened each story and paid special attention to the locations. Sure they were all from the same city but two different zip codes. Curiosity got the better of me so I started experimenting. I found that if write the different zip codes for the same city it looks like you can write more stories. A few times the city didn’t come up by zip code, but this is probably how more than 5 stories per location are written. The system must distinguish each zip code a different location. Just a thought.
On a side note, I still have issues with not being able to write 5 stories on Fargo. And today I tried to write my 5th story on a city and it won't let me. I'm 100% sure I have only written 4.
I am not sure about how the zipcode thing works, but let me share some of my experiences. I try to write 5 stories for any given city which is maximum allowed. I had experience that I could write more than 5 stories for a few times without knowing it is more than 5, but perhaps it was because of occasional glitch in the system that allowed me to do that. After organizing things what I do, I am staying on top of the stats how many stories I write for any given city.
Some of the cities in Japan has same name for the city and the prefecture. Tokyo is a good example. I have traveled to Tokyo numerous times and initially wrote 5 stories and maxed out. But, then I realized there are many cities in the Tokyo Prefecture including Shinjuku City, Shibuya city, Chuo City, to name a few. This essentially allowed me to share a lot moe stories than 5 for Tokyo. It is just like many small suburban cities in American cities. Stories can of course be written for each city 5 times. I found a few other cities in the world are like this, but not that many.
In many cases, no matter how big the city is, you are limited to write 5 times. For exmaple, Paris, London, Beijing, Seoul, Bangkok are all humongous cities, but there is no way to write more than 5 stories as there is no other smaller cities in those cities.