Hi there, @Silver Bullet.
I'm here to help share some clarification about manually entering bank transactions in QuickBooks.
Manually uploading your bank transactions may create duplicate transactions if those transactions from 1/21 to 1/28 will come through automatically.
You can always clear them out easily by checking off any duplicates you see under the For Review tab of your Banking screen, then click the Batch actions button and select Exclude Selected.
If you manually enter the missing transactions and match them, you'll just need to exclude the transactions that come in once your AMEX feed is restored.
Let me know if this works for you. I'll be here to help if you have additional questions about your bank feeds.
