If you contributed to the 401(k) plan in 2018, you were covered by the plan for 2018.  Depending on when you stopped contributing an the ending date of the plan year, you might also be covered for 2019, but not for 2020 and beyond.  Of course if you don't have compensation in 2019 and 2020 to support a traditional IRA contribution, you won't be making IRA contributions for those years anyway.