Hi Kim:
Do you have a copy of the AR data as of the Year-End? If it's in a different folder on your computer, point AR at it. If it's on a backup such as a tape, restore it to a different folder - Do NOT restore it to your current live folder. Point AR at that new folder and print the report.
Have you run a Period End since your Year-End? Did you use a "Transaction Clearing Date" later than the last day of the previous fiscal year? If you're like most people, the answer is "Yes" to both questions.
The Period End process transfers paid Invoices from Current to Historical. You can see this if you look at the "Transactions" tab for one of your Customers. Some transactions are in Current while older ones appear in Historical.
Unfortunately the AR Trial Balance report can only report on the Current table. This is why you are missing invoices.
Softrak is designing AR 9.0 right now and I believe that this is one area that will be improved.