Can I add old invoices that I have already been issued/paid by my clients from before I had Quickbooks so that my books show the entire year?

You may consider 2 options :

1. Record them as Invoices and Receive Payments

2. Record them as Sales Receipts

You will need an importer tool to speed up your work.

https://transactionpro.grsm.io/qbo

Joining the thread to share some more information about adding old paid invoices, @lorena-violetage.

Fiat Lux - ASIA's answer is correct. You can use both methods of adding invoices or recording them as sales receipts. Please be reminded that these are posting transactions an will affect your register balances.

For more information about these entries, I've added these links for you:

• What is the difference between an invoice, sales receipt, bill, and statement?
• Invoices vs sales receipts: which to use when

To add the transactions, go to the + New icon in QuickBooks and choose the transactions you want to record.

Please come back here if you require further guidance with recording sales transactions in QuickBooks. I'll be right here to help.

Thank you so much for the reply! I've added the invoice in as a 'sales receipt' however I am stuck on the section that asks "Deposit to:" - If this previous invoice was already paid months ago by ACH into my bank account, would I still select "Cash"?