Both Forms 5498-SA are correct due to the oddities of the way that Form 5498-SA must be prepared. Box 2 is required to show contributions made in a particular year, regardless of the year for which the contribution is made. Box 3 shows the amount of contributions made for a particular year after December 31 of the year for which the contribution is made.
In your wife's case, Box 3 of the 2020 Form 5498-SA shows that a contribution for 2020 was made in 2021 and was not included in box 2 because it was not made in 2020. Assuming that no contributions were made for 2019 in 2020, your wife's contributions for 2020 are the sum of the box 2 and box 3 amounts on the 2020 Form 5498-SA. Box 2 of your wife's 2021 Form 5498-SA properly includes the $20 contribution made in 2021 for 2020 as well as any contributions made in 2021 for 2021.
To determine from Forms 5498-SA the amount contributed for any particular year, you must subtract from the box 2 amount shown in that year's Form 5498-SA any amount in box 3 of the previous year's Form 5498-SA. In your wife's case, to determine the amount contributed for 2021 you must subtract the $20 shown in box 3 of the 2020 Form 5498-SA from the amount shown in box 2 of the 2021 Form 5498-SA. Since no contributions were made for 2021, your wife's 2021 Form 5498-SA should have $20 in box 2.
