Do commercial flight numbers often have city changes?

I have a flight booked Cincinnati to Atlanta to Tampa two weeks from now. I have a tight 40 minutes to change planes in Atlanta. So I had the idea to watch the earlier flights and note if they were on time or late and how far apart the gates for arrival and departure are. Turns out my Atlanta incoming flight is currently doing a Detroit to Nashville schedule. I was surprised to see Delta change the origin and destination for a commercial flight. Is this common?

No, it’s not common. Many flight numbers are “in the system” and have been used unchanged for years. Are you checking your route by flight number or some other way, e.g. by aircraft tail number?

flight number, I see where Wednesday, April 9, the flight now matches my flight schedule on the 17th.

It’s very common to see a variety of flight numbers operate the same city pair at approximately the same time on different days for the same airline.