I hope this helps: "for 2020 there was only unemployment"

We had a great comment here (to paraphrase): $0 is less than any other amount of earned income.

It might help if you drop the consideration of Unemployment entirely. The EITC lookback has nothing to do with Unemployment. It isn't "only my clients with unemployment" but that seems to be what you are using in your analysis.

It simply needs you to identify is Less Earned Income in which year?

Stop worrying about how Unemployment fits into this, because it doesn't apply at all. The tax payer can have had no unemployment funds, and you still do the analysis.

Don't forget your IRS resources:

https://www.irs.gov/newsroom/eitc-awareness-day-critical-tax-credit-provides-a-significant-refund-bo...

https://www.irs.gov/credits-deductions/individuals/earned-income-tax-credit-eitc

https://www.irs.gov/credits-deductions/individuals/earned-income-tax-credit/who-qualifies-for-the-ea...