I'm here to make sure you can successfully record last year's transactions, @Ana H.
If the date of the transaction you are attempting to generate is earlier than the As of date of the inventory item, a warning will show. Please make sure that the date of the transaction matches the day you began keeping records of the quantity of this item you have on hand.
To do this, please follow the steps below:
- Go to the Gear icon.
- Select Products and Services under Lists.
- Select the item and click on Edit.
- Click on Starting Value in the Quantity on hand section.
- A message will prompt. Click Got it!
- Review the As of date of the item and compare it to the date you selected.

Additionally, I've added an article that'll help you run reports to keep track of the status of your inventory such as the best sellers, what's on hand, the cost of goods, and more: Use reports to see your sales and inventory status in QuickBooks Online.
Please don't hesitate to hit on the Reply button if you need further assistance in managing your inventory items in QBO. I'll be right here to help you thoroughly. Take care and have a good one.