What the tax experts above are telling you is this:
When you are completing your TurboTax return, the program is continuously trying to add things to get you more refund.
When you start the questions on the Recovery Rebate Credit, the software initially adds the full amount to your anticipated refund amount until you actually get to the questions about the amount you actually received in the first and second stimulus checks. Once the software finds out that you already received a stimulus check that they already added to your refund amount, then they have to adjust it back out in order too have an accurate amount when you get to the end of the return.
If you are entitled to some additional stimulus money, then it will add it into your anticipated refund amount.
If you noticed that you ended up losing part of the anticipated additional stimulus check (since you had already received the checks) but not all of it, then you must have been entitled to receive the amount received plus an additional amount based on the IRS calculations determined in advance by the Internal Revenue Tax Code but not the full amount again. That is when it was reduced by $400 but not the full $1000 from your comments above.
The IRS has guidelines in the Internal Revenue Tax Code that determines how to calculate the amount to be received based on the information filed in your returns filed.
