It makes complete sense that Kia might want to start a 2021 MY (model year) in 2020 if for no other reason than to be competitive with other mfgs who are likely introducing 2021s in 2020. For whatever reason, customers always want the latest/greatest and if everything else is equal in fall of 2020 between two cars, the one with the 2021 label will be perceived to be newer. In the short term, the resale value of the later MY will also be higher.
And it may not be exactly the same car..... mfgs tend to bundle up small improvements and roll them out on the MY boundaries just to make inventory control, parts, service info, etc. manageable. Even if Kia is keeping the basic car unchanged, there may be some improvements under the skin. Or they may juggle colors, trims, option packages, etc. to meet customer preferences.
The fact that Kia rolled out a 2020 in March of 2019 may push them to also roll out the 2021 MY a little earlier than the typical fall timing just to not have the same MY on the market too long. By law, you're allowed to ship a MY for year X on Jan 1, X-1.
- Mark