Hello there, @manijojo. I'm here to help you add your client's data to their QuickBooks Online (QBO) account.
Yes, you can start adding transactions for each year in the QBO company and close the books to prevent changes to past entries. Then, repeat the process until you're in the current year. Before that, please read the details in this link to further know what happens when you close your books: What changes after year-end close.
You can also check this guide to help you manually import old data into the QBO account: Common questions about importing data to QuickBooks Online.
I've also attached this helpful resource to provide additional assistance in navigating QBO: Getting Started in QuickBooks Online.
If you have any other concerns about managing the data of your client, please don't hesitate to post again here. I'll be right here to back you up. Have a great week ahead and keep safe always.
