You essentially renew uniforms with Nike like you renew a contract. So every 4 years er so, the schools like ISU, Iowa, etc renew jerseys. Any big changes to the base uniform design will be made after that time period. Now, that doesn’t mean you can’t get some alternate uniforms thrown in every year. Very expensive though and you usually have to buy helmets to go along with the alternates if you want to do it right, and most schools run some sort of marketing campaign alongside the “new” uniforms.
Obviously the “elite” Nike schools are able to roll out new uniforms left and right in basketball and football and don’t wait that 4 year or whatever period. I’d expect new football uniforms in 2 years (however I do think we’ll get a nice alternate this year or next) and then basketball will get new uniforms for 2022 and we'll definitely be getting a black uniform and I’m hoping a throwback.