Hi there TNB Neil,
It's important that all your transactions are entered correctly for your books to be well balanced. QuickBooks Desktop is a great tool able to help you keep track of sales and expenses so you can see the profit of your company. I can point you in the right direction for assistance with reports.
For assistance with reports not showing properly when the data is grouped by customer, I recommend reaching out to the QuickBooks Desktop support team outside of the Community. They'll be able to view the affected reports and transactions with you in a secure setting to help make sure they appear correctly. You can reach them using the options outlined in the QuickBooks Desktop software support policies.
If you have any other questions, feel free to reach out here.