In 2020-2021, Texas Tech and Oklahoma both had 9-8 records, finished 6th and 7th in conference, Texas Tech was a 6 seed, Oklahoma an 8.
In 2019-2020, only 2 teams were above .500 in conference play. There was no tournament so no seeding to go off.
In 2018-2019, Iowa State was 9-9 in conference and finished 5th out of 10, a 6 seed.

Below is the last time every Big 12 team (current and incoming) was in the NCAA tournament. This is perhaps the most crazy thing to me, every team has been in at least one of the last 3 tournaments.
2021 - Kansas, Texas, Oklahoma, West Virginia, Oklahoma State, Texas Tech, Baylor, BYU, Houston
2019 - Kansas State, Iowa State, Cincinnati, UCF (again, there was no tournament in 2020)
2018 - TCU