in both years there was a point in the TT interview where you were to tell TT how much stimulus you ALREADY received. if you failed to do that, your refund on your tax return was inflated. Since the IRS knows how much they sent you, they compare what they know they sent you versus what you reported they sent you. If that does not match, then your refund is reduced by the difference because, in essence, you are trying to claim the same benefit twice.
by chance did you file a joint return? if so, there were two letters, one sent to you and one sent to your spouse. In TT, you were to enter the SUM of BOTH letters; I see many posts where taxpayers didn't realize they needed to add the two letters together. Since both letters had the same amounts, it was easy to assume they were duplicate letters and / or the spouse who filled out the tax return didn't realize the other also received a letter.
