The fact that you got a paycheck in January 2020 is not the only factor in determining whether or not you were covered by a workplace retirement plan for 2020. Even if you got no paycheck in 2020, you would still be covered for 2020 if this employer's plan year was not a calendar-year plan but instead used a fiscal year ending with some month other than December. If that's the case, your pay in December 2019 would have contributed to you being covered for 2020 even though it was earned and resulted in additions to the plan for your benefit in 2019.
