I retired in 2018, I have a 401K. No Pension. So now that I am not working I can answer the question "Is David covered by a work retirement plan?" No. Correct?

Being covered goes by the year, so, if you received a W-2 and the checkmark for retirement plan in Box 13 is checked then you are covered for the year.

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.