In my science fiction writing, I've a 29th century British colony on one planet and had to come up with a modification of the union jack to fit their feisty independence -- following the model of superimposing new attributes onto the existing flag. And now I find that I've done as "good" a job as they did originally. (grin) Believable world building is in the details, whether you include them in the stories or not. (double-grin)
Dr. Phil