This isn't a program issue. It's how the IRS has instructed that the credit work.
The checks are paid to or for specific dependents. They are issued based on your total circumstances at the time of issuance, and what you qualify for in that "snapshot" of time. If you hadn't added a dependent this year, then you would have technically received an overpayment - but the law says they can't ask for that back. When you were paid your advance payment you had yourself + X# qualifying dependents. When you file your tax return, the calculation is the same (it's the number of dependents claimed, regardless of who they are) whether the dependents are the same individuals that received prior payments before. The only "individuals" tied to payment are the primary taxpayers. The rest are just numbers in the system.
