US flag matters -- going off from the real world, into speculative fiction... considerable play is made with these things, in Harry Turtledove's "Southern Victory" alternative-history novel series. The premise: the Confederacy wins the Civil War in 1862, and successfully secedes -- there ensues a protracted rather nasty situation, in which the United States and the Confederate States are permanently at each other's throats, and fight war after war with each other.
In this time-line of Turtledove's, the "political" map differs considerably from that in "our time-line". For whatever reason, there are overall fewer separate states in the United States -- for instance, North and South Dakota are just the one state of Dakota. Various states on the USA / CSA border change hands, or appear / disappear, from time to time. IIRC -- Puerto Rico, as mentioned in PPs, still belongs to Spain in this time-line, in which there is no Spanish-American War. Certainly, in Turtledove's time-line, Alaska is still Russian territory.
What with all the above, it can be something of a puzzle to keep track of how many states the United States has, at any particular point in time. People who are geeks over this series, have lots of fun homing in on references in the text, to the number of stars on the United States' flag, and discoursing / disputing over whether the cited number is in fact correct...