The two checks were issued based on the data on the 2018 or 2019 tax forms, but the final decision on the amount of the tax cut is based on the 2020 tax forms.
Therefore some didn't get checks and will now be made whole; some got checks but they were too small and will now be made whole; some were overpaid and are not required to pay back the government; and as what happened to me: one was too large based on 2018 numbers, the other was too small based on 2019 numbers so I don't have to pay back the overage, and they will make me whole on the 2nd check.
Many families found that their kids were too old to get the dependent check during 2020 based on the 2018 or 2019 forms because they were still a dependent in the eyes of the tax code, but wouldn't be a dependent based on the 2020 forms. These children should get a tax credit to cover the amount they qualify for based on their 2020 numbers.
The key for your situation is that they can't claim you, not that they didn't claim you. In your case, having moved out makes it easier to prove you aren't a dependent.
The recovery rebate credit is the section of the tax forms you are interested in. In a nutshell you calculate what you should have received from each check, and then compare it too what you did receive.
Some people should have received the 2nd check, and didn't because the IRS ran out of time. They stopped sending funds in mid-January. These people will also use this section of the tax forms to get any funds that fall into this category.