I can see the urgency of keeping your client's financial data accurate, @rshires. 

Let's make sure your Report period sets for the Next Calendar Year or Last Fiscal Year date so your client's Retained Earnings account will show up in the Balance Sheet report in QuickBooks Online (QBO).

You're on the right track in updating your client's Accounting preferences on the Account and Settings page. However, modifying your fiscal year-end date won't change any data in your client's account. The effect is not retroactive, especially when viewing your previous years' data.

Thus, the update will affect report dates when generating new sets of reports or budgets. To check your client's net income as Retained Earnings, pull up a Balance Sheet report (from the Reports menu) and set the Report period for the Next Calendar Year or Last Fiscal Year. Please see the screenshot below for your reference.

You can read this article to learn more about the Retained Earnings account in QBO: How to review Retained Earnings account details.

Also, you may want to check out this article as your reference to guide you in closing your books to prevent unwanted changes before filing your taxes in QBO: Close your books in QuickBooks Online.

Please let me know if you have other concerns about the Retained Earnings account and keeping your client's data accurate in QBO. I'll gladly help. Take care, and I wish you continued success, @rshires.