Hello there, peterguterman,
If the inventory item is dated for February, you're unable to create invoices dated prior to that date. You'll encounter this error, "Please select a transaction date that comes after the date you started tracking the quantity on hand of these inventory items."
To create January invoices, you'll want to create a new item and make sure it's dated for January. Here's an article for creating items: Add inventory products in QuickBooks Online.
Check out these articles for future reference:
Let me know if there's anything else you need help with.