Hello there, @BernieJ.
You'll want to make sure that the starting date of the FIFO is prior to the transaction dates. Let me provide additional information about Average Costing vs FIFO.
QuickBooks will depend on the start date you've selected when switching to FIFO. Those items used before the start date of the FIFO will fall under the Average Costing.
Any existing balances of items on hand at the date that FIFO is enabled are placed into one costing layer. Also, please know that the report only includes balances and transactions from the date of when FIFO began.
For additional information, feel free to check out these articles:
You might also want to read this article to know how QuickBooks tracks inventory: Understand inventory assets and cost of goods sold tracking.
Please know that you can always get back to here in the Community if you have any other questions. I'll be standing by for your response. Have a great day.